Without even a wince, Bill Blackton slides a 16-gauge needle into his right forearm and begins the ritual that has saved his life about 3,000 times since his kidneys failed 20 years ago.

He runs down a mental checklist with the methodical calm of an airline pilot, checking dials, gauges, clamps and coils of plastic tubing connecting him to a four-foot-high machine in the study of his Arlington townhouse.

The machine is a fancy pump. Its centerpiece is the dialyzer, an artificial kidney shaped like a flashlight, which does what Blackton's own kidneys stopped doing in 1965: filtering from his blood the deadly wastes the body's cells create simply by living.

Blackton, 38, has been on dialysis for more than 20 years, longer than anyone else in the Washington area and all but a few in the world.

"There are probably not more than 10 in the world" who have survived that long on dialysis, says Dr. Belding Scribner, professor of medicine at the University of Washington in Seattle. Scribner's invention of the arteriovenous (A-V) shunt 25 years ago revolutionized treatment of kidney disease by enabling patients to use the artificial kidney over and over again without wearing out their blood vessels.

Blackton rechecks the dials and presses the "on" button. Blood starts rushing through a plastic tube, detouring out of his forearm, through the artificial kidney and back into a vein in his arm.

"Now, I just sit here for four hours," he says matter-of-factly, settling back on the bed and adjusting the volume on the Phil Donahue show by remote control. Beside him on the bed is a tray of brunch: a salad, a dish of pineapple and a plate of rolls.

He's done this so many times it's easy to forget that if he didn't, he would die. Until 1960, when the A-V shunt was developed, there was no hope for patients with irreversible kidney disease.

Today, about 72,000 Americans receive dialysis treatments three times a week. Most visit a hospital or kidney center; fewer than 20 percent dialyze themselves at home, as Blackton does.

Each dialysis treatment takes four hours, but it's neither painful nor grueling.

Three days a week, "I come home from work, go on the machine, turn on the TV, get the paper," Blackton says. "It's sort of enforced relaxation."

Dialysis works on the principle of osmosis. The cylindrical artificial kidney is packed with cellophane-like, semipermeable membranes.

On one side of a membrane is the blood. On the other side is the dialyzing fluid, which flushes out the toxins as the blood circulates past. Microscopic pores in the membranes allow wastes to pass through without drawing off vital ingredients.

Blackton loses about five pounds in wastes and excess water during each dialysis session.

It's midway in what he calls "the four-hour run," and Blackton is bored. The odometer on the back of the machine passes 4,827 -- the total number of hours he's been on dialysis since he got this machine seven years ago.

"The measure of the success of dialysis is that they've made it boring," he says, paraphrasing Norman Mailer's comment about the space program.

Even sticking himself with 16-gauge needles, about the same diameter as pencil lead, has become routine. But it wasn't always this way.

"It's a highly unnatural act," he acknowledges.

At first, a doctor or a nurse always inserted the needle for him, because he couldn't bear to do it himself. He considered taking a scholarly approach, getting a textbook and studying veins.

"But there was this one nurse who was strong-willed, and one day she just handed me the needles and told me to do it. She helped me, and I did it.

"On my own, it would have taken months."

Now it's almost second nature. He could hit the vein in his sleep, he says, and it upsets him more to watch someone else put the needle in than to do it himself.

Twenty years ago, just out of high school, Blackton suddenly started feeling sick. He was anemic, constantly tired. He lost his appetite and his blood pressure rose.

He wound up in the hospital for tests, and a doctor finally told him his kidneys had shut down. Kidney disease, which is hereditary, ran in his mother's family, but his parents hadn't warned him for fear of worrying him needlessly.

If his disease had shown up five years earlier, before dialysis became available, Blackton would not be alive today. But his doctors hooked him up to a dialysis machine and restored him to health.

Dialysis was more of an ordeal in those days. Infections and side effects were common, and survival rates were lower. Many patients died of high blood pressure, which today can usually be controlled by drugs.

Blackton would go to Kings County Hospital in Brooklyn and stay overnight, because dialysis took up to 20 hours. The machine was huge, noisy and crude. The tube carrying the outflow of filtered waste led right out the window of his second-floor room.

"I don't think anything grew out there," he says.

The home dialysis pump Blackton uses today is smaller, quieter, more mobile and more efficient, with more safety alarms and "dashboard" features -- what Blackton calls "bells and whistles."

During the treatment, Blackton can't stray more than a few feet from the machine -- the length of the tubes sticking out of his arm. But in an emergency, he can briefly disconnect himself.

"It's got to be for something really important -- you know, like a diet Pepsi or something," he jokes.

Each home dialysis treatment costs about $100, about half of which is due to the dialyzer, which must be replaced each time. In a year, that amounts to about $15,000, of which Medicare pays 80 percent and Blackton's private insurance pays the rest.

Dialysis in a hospital or kidney center costs even more -- between $25,000 and $30,000 a year. But Congress amended the Social Security Act in 1972 to extend Medicare coverage to kidney dialysis patients.

For dialysis patients like Blackton, the only alternative to thrice-weekly dialysis is a kidney transplant. But a transplant, which requires a donor with closely matched blood and tissue type, carries no guarantee.

Blackton received a kidney transplant in 1970, but his body rejected it gradually, and it was removed a year and a half later. (He still has his own two kidneys.)

But even before his body rejected the transplant, the powerful drugs he had to take to suppress his immune system and reduce the chances of rejection caused unpleasant side effects. He gained weight, his muscles atrophied, he developed small cataracts in his eyes, and he was moody from the drug-related hormonal changes.

For now, he's satisfied with dialysis, despite the time it takes. He doesn't rule out another transplant, but wants to wait until further progress eliminates the need for such powerful immunosuppressive drugs with their side effects.

Dialysis is no picnic, but Blackton manages not to let it interfere unduly with his normal life. He works full-time as a writer for Voice of America. He keeps in shape by swimming and riding an exercise bike. His bookcase is festooned with jersey numbers from all the fun-runs he's completed. He's rarely sick.

He is frustrated with the public's tendency to view dialysis patients as helplessly dependent, chronically ill people tethered to a machine.

For years, because of that public image, Blackton was what he calls "a closet dialyzer."

"I used to tell nobody," he says.

Today's he's more open. He doesn't make a big deal out of it, but he doesn't hide it either. And he refuses to let his kidney disease control his life.

"Sure, I get tired of doing dialysis," he says. "It is a drag. But it's manageable. I just work around it."