SHANGHAI — Sheng Huizhen’s life story is typical of immigrants who succeeded in America. After getting her PhD in biochemistry, she landed a job as a postdoctoral researcher at the National Institutes of Health. She got a green card, bought a house in Maryland, and worked her way up to visiting associate, senior staff fellow, and, finally, the prestigious position of staff scientist.

But then she moved back to China. A federal law prohibiting the use of public money for research on human embryos prevented her from doing the kind of work she wanted to do. The Chinese government enticed her to return with $875,000 for a new laboratory she could use to do her research.

“Due to different culture and religious background, the public in China are more friendly for stem-cell research,” Mr. Sheng, 55, whose family remained in the United States, said.

Lured by grants, tax breaks, looser regulations, and a scientific environment more open to certain types of experiments, China’s long-lost scientists are coming back in droves. As the NIH and other American research institutes complain about the tightening of in the nation’s scientific budget, China has announced that it will double its research-and-development spending by 2010, to about $69 billion.

The returning scientists are reversing a trend that began in 1978, when communist China first allowed students to go abroad. It used to be that when they left, they left for good. But in recent years, more than 275,000 have come back.

Many of these “sea turtles,” as they are known, have returned with doctorates in science or engineering and are going to the Chinese Academy of Sciences, the government-affiliated research institute, where 81% of the members are returnees. Fifty thousand of the returnees are starting their own companies, according to China’s Ministry of Education, pushing the boundaries of innovation and of what’s acceptable in medical science.

For example, Jiang He, 50, was a researcher at the NIH’s National Heart, Lung and Blood Institute until 1999. The former Potomac, Md., resident is now chief executive of Frontier Biotechnologies in the central metropolis of Chongqing. The company works on anti-HIV products.

“If I started all from scratch in the United States, I would have spent much more time looking for funding,” Mr. Jiang said. “I probably could get only a few hundred thousand dollars and could only afford a couple of researchers. … Here we have 30 to 40 employees.”

Ni Jian, 44, was a postdoctoral fellow in tumor research at the National Cancer Institute in Bethesda, Md., and then went to work as a scientist at Human Genome Sciences in Rockville, Md. He is now the head of Human Antibodomics, a company in the eastern city of Suzhou that harnesses antibodies to treat diseases like cancer.

Mr. Ni said he initially thought he’d stay in America forever. But a tycoon in China with liver cancer was looking into investing into a biotech company and approached him. Then the city of Suzhou gave him about $280,000 for his company and $130,000 for an apartment and cars.

They were offers he couldn’t turn down. “Low cost, easy access to clinical materials, government funding, and collaboration with experts are all advantages,” he said.

Jin Lei, 54, was in America for eight years, at the National Institute of Environmental Health Sciences in North Carolina. He returned to China in 2001 to work on bioprosthetic heart valves.

Mr. Jin, who founded Beijing Biren Medical Technology, said the speed at which science is allowed to move in China is the main attraction for basing a company here.

“If I were in the United States, I think I’d never be able to create this company,” Jin said.