The president of MIT expressed regret that researchers from the school apparently experimented with radioactive materials on retarded youths without the subjects' consent.

"I was sorry to hear that at least some of the young people who participated in this research and their parents apparently were unaware that the study involved radioactive tracers," Charles Vest said of tests in the 1940s and 1950s at a state school for the retarded."People should not unknowingly become the subjects of research studies of this type," he said in a statement late Friday.

Vest said an internal review concluded the radiation exposure slightly increased the subjects' chance of developing a fatal cancer, but the increases were extremely small.

Vest said the studies were designed to promote health through better understanding of nutrition. The radiation exposure appeared to have been well within current acceptable limits, he said.

More than 100 residents of the Fernald State School in Waltham were fed or injected with radioactive calcium and iron during at least six studies by Harvard University and Massachusetts Institute of Technology researchers from 1946 to 1956. Radioactive forms of the minerals were used so scientists could trace how they were digested and absorbed.

The levels of radiation to which test subjects were exposed were 30 to 99 percent below current limits allowed in research, Vest said in another statement Saturday.

MIT's vice president and dean for research, physics Professor J. David Litster, reviewed four articles in professional journals and one doctoral thesis based on the studies for information about radiation exposure, Vest said.