THE OPERATING ROOM was nothing nearly as grand as the one in which U. S. Robots and Mechanical Men had performed its various upgrades on Andrew in recent years, but Andrew could tell that the facility was superbly equipped and completely equal to the task. He looked with admiration and approval at the laser bank, the board of measuring dials and control panel, the spidery maze of auxiliary needles and tubes and pipes, and the main surgical stage itself, dais and bed and lights and instruments, white linens and dazzling chrome-steel fixtures, everything in readiness for the unusual patient.

And the surgeon himself was magnificently calm. Quite clearly he had been able in the interim to resolve whatever conflicts he had felt over the irregularities of Andrew's request and the ambiguities of Andrew's appearance, and now he was focused entirely on the professional task at hand. Andrew was more than ever convinced that he had made the only possible choice by selecting a robot surgeon to perform this operation.

Still, he felt a flicker of uncertainty-just a flicker-as the actual moment for the start of the operation arrived. What if something went wrong? What if he came out of the operation incapacitated in some way? What if the operation failed and he terminated right on the operating table?

No. None of that mattered. There was no way for the operation to fail, none. And even if it did-no. That simply did not matter.

The surgeon was watching him carefully.

"Are you ready?" he asked.

"Absolutely," Andrew told the surgeon. "Let's get down to it."

"Very well," said the surgeon phlegmatically, and with a quick, sweeping gesture took his laser-scalpel into his splendidly designed right hand.

Andrew had chosen to remain completely conscious throughout the entire process. He had no wish to shut down awareness even for an instant. Pain was not an issue for him, and he needed to be certain that his instructions were being followed precisely. But of course they were. The surgeon's nature, being robotic, was not one that would permit any capricious deviation from the agreed-upon course of action.

What Andrew was not prepared for was the unexpectedly intense weakness and fatigue that came after the job had been done.

He had never known such sensations as those that came over him in the early hours of his recovery period. Even when they had transferred his brain from the robot body to the android one, Andrew had experienced nothing like this.

Instead of walking normally, he lurched and staggered. Often he felt as though the floor before him was rising up to strike him in the face. There were times when his fingers trembled so violently that he had difficulty holding things. His vision, which had always been flawless, suddenly would grow blurry for long minutes at a stretch. Or he would try to remember someone's name, and nothing would come to mind except a tantalizing blankness that glimmered at him from around the corners of his memory.

He spent an entire afternoon, the first week after the operation, searching his mind for the full name of the man he had known as Sir. Then, suddenly, the name was there: Gerald Martin. But now Andrew had forgotten the name of Little Miss's dark-haired older sister, and it took him hours more of diligent searching before "Melissa Martin" popped abruptly into his brain. Two hours! It should not have taken him two milliseconds!

It was all more or less what Andrew should have expected, and in an abstract way he had expected it. And yet the reality of the feelings themselves was far beyond anything that Andrew had anticipated. Physical weakness was something new to him. So were poor coordination, uncertain reflexes, imperfect eyesight, and episodes of impaired memory. It was humiliating to feel so imperfect-so human

No, he thought.

There is nothing humiliating about it. You have everything backward. It is human to feel imperfect. That was what you wanted, above all else: to be human. And now that is what you are. The imperfections-the weaknesses-the imprecisions-they are the very things which define humans as human. And which drive them to transcend their own failings.

You never had failings before, Andrew told himself. Now you do, and so be it. So be it. You have achieved the thing you set out to accomplish and you must feel no regrets.

Gradually, as one day slid into the next, things began to improve.

Gradually. Very gradually.

The memory functions returned first. Andrew was gratified to discover that he had full access again, instant and complete, to the whole of his past.

He sat in the grand high-winged chair by the fireplace in the great living room of what once had been Gerald Martin's house, and let images of years gone by play through his mind: the factory where he had been constructed, and his arrival at the Martin house, and Little Miss and Miss as children, walking with him on the beach. Sir and Ma'am at their dining table; his wooden sculptures and the furniture he had made; the U. S. Robots executives who came west to inspect him; his first visit from Little Sir; the time he had decided at last to begin wearing clothing; Little Sir's marriage and the birth of Paul Charney. Even less pleasant things like the episode of the two louts who had tried to disassemble him while he was on the way to the public library. And much, much more, nearly two hundred years of memory.

It was all there. His mind had not been permanently impaired, and he was tremendously relieved.

The floor stopped trying to jump up and hit him. His vision stopped playing tricks on him. His hands finally stopped their infuriating shaking. When he walked, he was no longer in danger of stumbling and falling. He was himself again, in most of the essential ways.

But a certain sense of weakness still remained with him, or so he thought: a pervasive chronic weariness, a feeling that he needed to sit down and rest awhile before going on to whatever might be his next task.

Perhaps it was only his imagination. The surgeon said that he was recovering quite well.

There was a syndrome called hypochondria, Andrew knew, in which you felt that you were suffering from conditions that in fact you did not have. It was a fairly common thing among human beings, he had heard. People who were hypochondriacs found all manner of symptoms in themselves that no medical tests could confirm; and the more thought they gave to the possibility that they might be ill, the more symptoms they discovered.

Andrew wondered whether in his long unceasing quest to attain full humanity he had somehow managed to contract a case of hypochondria, and smiled at the thought. Quite likely he had, he decided. His own testing equipment showed no measurable degrading of his performance capabilities. All parameters were well within permissible deviation. And yet-yet-he felt so tired

It had to be imaginary. Andrew ordered himself to give his feelings of weariness no further thought. And, tired or not, he made one more journey across the continent to the great green-glass tower of the World Legislature in New York to pay a call on Chee Li-hsing.

He entered her grand and lofty office and she beckoned him automatically to a seat before her desk, the way she would have done with any other visitor. But Andrew had always preferred to stand in her presence, out of some obscure impulse of courtesy that he had never tried to explain to himself, and he did not want to sit now-especially not now. It would be entirely too revealing to do that Nevertheless, he found after a moment or two that standing seemed a bit troublesome to him, and he leaned, as unobtrusively as he could manage, against the wall.

Li-hsing said, "The final vote will come this week, Andrew. I've tried to delay it, but I've run out of parliamentary maneuvers, and there's nothing more I can do. It'll be voted on and we'll lose. -and that will be it, Andrew."

Andrew said, "I'm grateful for your skill at delaying things. It provided me with the time I needed-and I took the gamble I had to take."

Li-hsing gave him a troubled look. "What gamble do you mean, Andrew?" And then, with some irritation in her voice: "You've been so mysterious these past months! Hinting darkly at this or that big project, but refusing to let anybody know what it was that you were up to-"

"I couldn't, Li-hsing. If I had told you anything-or had said a word to the people at Feingold and Charney-I would have been stopped. I'm sure of that. You could have stopped me, you know, simply by ordering me not to proceed. The Second Law: there's no way for me to put up resistance against that Simon DeLong would have done the same. So I had to keep quiet about my plans until I had carried them out"

"What is it that you have done, Andrew?" Chee Li-hsing asked, very quietly, almost ominously.

Andrew said, "The brain was the issue, that was what we agreed-the positronic brain vs. the organic one. But what was the real issue behind that? My intelligence? No. I have an unusual mind, yes, but that's because I was designed to have an unusual mind, and after me they broke the mold. Other robots have outstanding mental abilities along one line or another, whatever specialty it is that they've been designed to perform, but basically they're pretty stupid things. The way a computer is stupid, no matter how many trillion times faster than a human it can add up a column of numbers. So it isn't my intelligence that makes people envious of me, not really. There are plenty of humans who can think rings around me."

"Andrew-"

"Let me have my say, Li-hsing. I'm getting to the point, I promise you."

He shifted his position against the wall, hoping that Li-hsing wouldn't notice that he didn't seem to have the strength to stand up unsupported for many minutes at a time. But Andrew suspected that she had already registered that fact. She was staring at him in an uncertain, troubled way.

He said, "What is the greatest difference between my positronic brain and a human one? It's that my brain is immortal. All the trouble we've been having stems from that, don't you see? Why should anyone care what a brain looks like or is built out of or how it came into existence in the first place? What matters is that organic human brain cells die. Must die. There's no way of avoiding it Every other organ in the body can be maintained or replaced by an artificial substitute, but the brain can't be replaced at all, not without changing and therefore killing the personality. And the organic brain must eventually die. Whereas my own positronic pathways-"

Li-hsing's expression had been changing as he spoke. Her face bore a look of horror now.

Andrew knew that she had already begun to understand. But he needed her to hear him out He continued inexorably, "My own positronic pathways have lasted just under two centuries now without perceptible deterioration, without any kind of undesirable change whatever, and they will surely last for centuries more. Perhaps indefinitely: who can say? The whole science of robotics is only three hundred years old and that's too short a time for anyone to be able to say what the full life-span of a positronic brain may be. Effectively my brain is immortal. Isn't that the fundamental barrier that separates me from the human race? Human beings can tolerate immortality in robots, because it's a virtue in a machine to last a long time, and nobody is psychologically threatened by that. But they would never be able to tolerate the idea of an immortal human being, since their own mortality is endurable only so long as they know it's universal. Allow one person to be exempted from death and everyone else feels victimized in the worst way. And for that reason, Li-hsing, they have refused to make me a human being."

Li-hsing said sharply, "You said you were going to get to the point Get to it, then. What is it that you've done to yourself, Andrew? I want to know!"

"I have removed the problem."

"Removed it? How?"

"Decades ago, when my positronic brain was placed in this android body, it was connected to organic nerves, but it remained carefully insulated from the metabolic forces that would otherwise have ultimately caused it to deteriorate. Now I have undergone one last operation in order to rearrange the connections along the brain-body interface. The insulation has been removed. My brain is now subject to the same forces of decay that any organic substance is vulnerable to. Things are set up now in such a way that-slowly, quite slowly-the potential is being drained from my pathways."

Chee's finely wrinkled face showed no expression for a moment. Then her lips tightened and she balled her hands into fists.

"Do you mean that you've arranged to die, Andrew? No. No, you can't possibly have done that. It would be a violation of the Third Law."

"Not so," Andrew said. "There is more than one sort of death, Li-hsing, and the Third Law does not differentiate between them. But I do. What I have done is to choose between the death of my body and the death of my aspirations and desires. To have let my body live at the cost of the greater death-that is the true violation of the Third Law. Not this. As a robot I might live forever, yes. But I tell you that I would rather die as a man than live eternally as a robot."

"Andrew! No!" Chee cried. She rose from her desk and went to him with astonishing speed, and seized his arm as though she were about to shake him. But all she did was grip it tightly, her fingers sinking deeply into his pliable synthetic flesh. "Andrew, this isn't going to get you what you want. It's nothing more than terrible folly. Change yourself back."

"I can't. Too much damage was done. The operation is irreversible."

"And now-?"

"I have a year to live, Li-hsing-more or less. I will last through the two hundredth anniversary of my construction. I confess that I was weak enough to time things so that I would still be here that long. And then-a natural death. Other robots are dismantled-they are irrevocably terminated-they are taken out of working order. I will simply die. The first robot ever to die-if, that is, it is felt that I am still a robot."

"I can't believe what you're telling me, Andrew. What good can any of this do? You've destroyed yourself for nothing-nothing! It wasn't worth it!"

"I think it was."

"Then you're a fool, Andrew!"

"No," he said gently. "If it brings me humanity at last, then it will have been worth it. And if I fail in achieving that, well, at least there will soon be an end to my fruitless striving and my pain, and that will have been worth accomplishing also."

"Pain?"

"Pain, yes. Do you think I've never felt any pain, Li-hsing?"

Li-hsing did something then that astonished Andrew beyond words.

Quietly, she began to weep.