Twice a week, nearly half of the 1,000 inmates at the Northern Nevada Correctional Center spend an hour-and-a-half watching soap operas while blood is taken from their arms, its plasma removed and the red blood cells returned to their veins.

Donating this blood is the only "job" most prisoners at the center have. For each donation, they are paid $5 -- all in quarters so guards can keep track of money caches. The prison profits, too; the private plasma-collecting company pays the state about $1 per donation.

The Nevada case is one of many examples of the booming entrepreneurial trade in blood, a strange side-effect of the epidemic of acquired immune deficiency syndrome, or AIDS.

Although plasma manufacturers used to be skittish about buying prisoners' plasma because of fears that a greater percentage of men in the high-risk AIDS groups live behind bars, worries have eased because blood and plasma now can be screened for the presence of AIDS antibodies.

Selling prisoners' plasma, which began in 1966, was halted more than a decade ago, but now the prison blood trade is booming, with 15 centers nationwide and several others in the planning stage. In the last few months, Iowa, Missouri and Idaho have allowed plasma companies to set up their stretchers in prisons, joining others in Arizona, Arkansas and Louisiana.

Plasma is blood without the red cells but containing many important ingredients, including antibodies and the clotting factor that can prevent fatal bleeding. Plasma is used in making vaccines and other medical supplies and has a ready market, according to Jerry Matlin, a lawyer for CTM Industries, which operates one of two Iowa plasma centers. "It's an expanding, growing industry," Matlin said. "We're just stuck with the PR image that used-car salesmen have."

Part of that negative image was promoted by the federal government, whose National Blood Policy of 1973 condemned blood that was sold by donors rather than given freely. The government said blood from for-profit firms was unclean. The policy caused blood-selling centers, including those in prisons, "to go the way of the dinosaur," said Matlin.

Some plasma centers survived and have prospered, in college towns and city storefronts throughout the United States. But now there has been a surge of interest in prison centers because of a reduced supply of plasma, wardens' eagerness to employ idle prisoners, and the state treasuries' revenues from the new blood business.

One reason for the drop in supply is that fear of AIDS contamination has led to use of virus-killing heat treatments, which reduce the volume, according to John Andervont, director of blood center licensing for the Food and Drug Administration.

Donors also were lost in recent years because of fears that blood donation is somehow linked to AIDS. Although there are no cases of donors acquiring AIDS, there have been cases of hemophiliacs who developed AIDS from contaminated blood products and instances of people, including infants, developing AIDS from blood transfusions.

Because prisons contain many members of the high-risk groups of homosexuals and drug users, plasma processors until recently were reluctant to buy prison plasma, as well as plasma from certain regions.

"You couldn't sell plasma that was coming out of San Francisco or the New York metropolitan area for all the tea in China," Matlin said. "Manufacturers were leery and you couldn't blame them."

But for some manufacturers, the undesirability of the walk-in "street center" blood made prison centers begin to look more attractive, Matlin said. Prison officials might know drug and sexual histories of inmates, and might screen donors better.

Another element of the prison plasma boom is cash. According to a 1984 American Correctional Association study, states can collect up to $200,000 a year from a plasma program. Arkansas, it noted, bought $185,000 worth of medical equipment from money generated by its prison center in Grady.

But some wardens said money earned by the state is spent hiring guards to monitor the operation. "Every now and again someone steals a syringe and we'll raise eleven kinds of hell to get it back," said John Slansky, director of the Northern Nevada Correctional Center.

Opinions on the plasma trade are divided. "The companies have salesmen out trying to convince the institutions to put it in," said George Sumner, Nevada's director of corrections. "If I had my way, I'd rather have real jobs for the inmates instead of selling their plasma."

Other corrections officials are more enthusiastic. "Inmates can use it the money earned for restitution, as well as their personal needs," said Hal Farrier, director of corrections in Iowa. "We're pleased to get some private industries involved with us."

Under federal law, prison plasma is used only in manufacturing medical products, such as rabies and tetanus vaccines and intravenous fluid for shock or burn victims.