Martin Rodbell, 73, a biomedical research scientist at the National Institutes of Health who won a Nobel Prize in 1994 for discovering a vital molecular mechanism that helps cells respond to stimuli, died Dec. 7 at the University of North Carolina Hospital in Chapel Hill. He had heart ailments.

Dr. Rodbell shared the Nobel Prize in physiology and medicine with Alfred G. Gilman, a Dallas pharmacologist, for work done separately during the 1960s and 1970s on a process that has come to be known by cell biologists as "G-protein" signal transduction. Dr. Rodbell did most of his research in this period at the NIH facility in Bethesda; Gilman was then a professor of pharmacology at the University of Virginia Medical School.

Their research demonstrated the role of G-proteins in cellular communication. The cells signal each other through a complex process that involves a series of chemical reactions, each altering the outcome of the next reaction. This process begins with the release of a hormone somewhere in the body and its distribution through the bloodstream. G-proteins enable the cells to receive and respond to the hormonal signals.

A similar process operates in the nerve endings of the eyes, nose and mouth, enabling these specialized cells to respond to such environmental stimuli as images, light, smells and flavors.

The research by Dr. Rodbell and Gilman demonstrated the fundamental importance of G-proteins to the cellular communication that is essential to the normal functioning of the body. It also has figured in knowledge about several diseases.

Some forms of cancer are known to be caused by overactive or mutated G-proteins. Diabetes and alcoholism are believed to result, in part, from impaired G-protein function. In cases of cholera, the bacterial toxin acts on G-proteins of the intestines, causing the continuous pouring out of water and sodium.

Dr. Rodbell was born in Baltimore. During World War II, he served in the Navy and the Marine Corps. He graduated from Johns Hopkins University and received a doctorate in biochemistry from the University of Washington.

In 1960, he became a research fellow at the National Institutes of Health in Bethesda, and he remained there for 25 years. He moved to North Carolina in 1985 as scientific director of the National Institute of Environmental Health Sciences at Research Triangle Park, and he retired there in 1994.

He retired, he said, because his research budget, which was aimed at basic science rather than any immediate practical goal, was cut repeatedly.

"The world ain't the same," he said at a news conference when his Nobel Prize was announced. "Now everything is targeted, bottom line, how to make a buck. The attention of the Congress and the executive branch always has been toward the end goal. They are not as willing to take a chance now on people like me in exploring the unknown."

In addition to his research at the National Institute of Environmental Health Sciences, Dr. Rodbell also was an adjunct professor at the University of North Carolina and at Duke University. Colleagues described him as passionate in his conviction that the study of living organisms should be about more than curing ills or making people feel better.

"While Dr. Rodbell's scientific genius is justly celebrated, we also remember his generous training of young scientists and intellectual stimulation of his colleagues," Carl Barrett, his successor as scientific director of the National Institute of Environmental Health, told the Associated Press.

Dr. Rodbell was one of six recipients of the 1998 North Carolina Award, which is the state's highest honor.

Survivors include his wife of 48 years, Barbara Rodbell of Chapel Hill; four children, Suzanne Richardson of Cabin John, Paul Rodbell of Silver Spring, Andrew Rodbell of Bethesda and Philip Rodbell of Hingham, Mass.; and seven grandchildren.