“Any reduction in the rate of development of drugs for these diseases will mean hundreds of thousands of people, really millions of people, dying because it would be years of delay,” he said.

If human lives can be saved, Dr. VandeBerg said, “it would be grossly unethical not to do research” on chimpanzees.

There are 1,000 chimps housed in research facilities in the United States, including at the New Iberia Research Center. The center, part of the University of Louisiana at Lafayette, occupies 100 acres in the heart of Cajun country about 130 miles west of New Orleans. It houses 360 chimpanzees, 240 of which belong to the university and 120 to the N.I.H., and more than 6,000 other primates, mostly rhesus macaque monkeys. It has faced accusations of chimp mistreatment in the past, and some violations of animal care standards were found, and corrected, according to Department of Agriculture inspections. The latest, in July, found some outdated drugs for the animals.

On a recent visit, some of the chimpanzees were in 34-foot-diameter geodesic domes, some in smaller outdoor cages, and some, less than 10 at that time, said Dr. Thomas J. Rowell, the director of the center, were in active studies and held in indoor cages about 6 feet by 5 feet and 7 feet high, one chimp per cage. The physical procedures involved in the studies, he said, involved injections, blood samples and liver biopsies, the latter done under sedation.

Many studies last only a couple of days, Dr. Rowell said, but a few are longer. A study near completion had been going on for four months. He passionately defended the center’s treatment of chimps, emphasizing the veterinary care and efforts to enrich the chimps’ lives with more interesting environments.

Using captive chimpanzees for research in this country dates to the 1920s, when Robert Yerkes, a Yale psychology professor, began to bring them into the country. During the 1950s, the Air Force began to breed chimps for the space program, starting with 65 caught in the wild. Chimps were also bred for AIDS research in the 1980s, which met a dead end. By the mid-1970s, support for preservation of threatened species had grown, and the importing of wild-caught chimps was prohibited. In 2000, a federal law was passed requiring the government to provide for retirement of chimps it owned after their use in experiments was over, and Chimp Haven opened near Shreveport, La., to care for these chimps and others.

It was an attempt to bring some semiretired chimps at the Alamogordo Primate Facility in New Mexico back into the research pipeline that prompted part of the recent surge of opposition. The N.I.H. wanted to move about 200 chimps it owned from Alamogordo to the San Antonio center, which is part of the Texas Biomedical Research Institute. The Humane Society lobbied to prevent the move, and the N.I.H. relented, asking the Institute of Medicine, an advisory board, for the report on chimps in experimentation this year.