While studying in Berlin as a National Research Council fellow (1932-33), Wald discovered that vitamin A is a vital ingredient of the pigments in the retina and, hence, important in maintaining vision. After further research in Heidelberg and at the universities of Zürich and Chicago, he joined the faculty of Harvard University in 1934.

By the early 1950s Wald had succeeded in elucidating the chemical reactions involved in the vision process of the rods (receptors on the retina used for night vision). In the late 1950s, with Paul K. Brown, he identified the pigments in the retina that are sensitive to yellow-green light and red light and in the early 1960s the pigment sensitive to blue light. Wald and Brown also discovered the role of vitamin A in forming the three colour pigments and showed that colour blindness is caused simply by the absence of one of them. Wald became professor emeritus at Harvard in 1977.

Wald contributed greatly to our knowledge of the human eye, particularly the visual pigments and how light affects them. He was on the forefront of the revolution that changed biology from a cellular to a molecular science. An early and outspoken opponent of the Vietnam War, Wald was always a lively, engaged, and formidable figure in the political arena.

Wald, who was also an outspoken opponent of U.S. involvement in Vietnam, retired in 1977 as the Higgins Professor of Biology at Harvard University, having held that chair since 1968. He spent 43 years doing research and teaching at Harvard, beginning as a tutor in biochemical sciences in 1934 and becoming a full professor in 1948.

When Wald received the Nobel Prize, he said pensively: "A scientist lives with all reality. There is nothing better. To know reality is to accept it and eventually to love it. A scientist is in a sense a learned child. There is something of the scientist in every child. Others must outgrow it. Scientists can stay that way all their= lives."

He shared the 1967 Nobel Prize in Physiology or Medicine with Dr. Haldan K. Hartline, a professor of biophysics at the Rockefeller University in New York, and Dr. Ragnar Granit, a Swede who was then a visiting professor of neurophysiology at Oxford University.

The three professors were honored for their discoveries about the primary chemical and physiological visual processes in the eye. They shared the prize money, which was the equivalent of about $61,700.

Wald was lauded by the Royal Caroline Institute in Sweden, which awarded the prize, as "one of the world's greatest authorities on the biochemistry of perception."

Wald's chief contribution was to help understand how light activates photo-receptive cells in the retina, causing the molecular changes that lead to impulses along the optic nerve to the brain.

Wald worked on the discoveries with his longtime collaborators, Dr. Ruth Hubbard, a biochemist whom he married in 1958, and Paul Brown, a scientific researcher.

Wald also carried out significant research about the way vitamin A affects vision and about the roles of various cells in the perception of colors and black and white vision.

In 1969 at the Massachusetts Institute of Technology, he gave a widely cited speech criticizing the Vietnam War and the arms race. "There is nothing worth having that can be obtained by nuclear war," he said.

In that address, Wald also criticized the Anti-Ballistic Missile Treaty, the peacetime draft and what he called the militarization of the United States. He decried the contention that "those are the facts of life."

"No," he told the audience, "those are the facts of death. I don't accept them, and I advise you not to accept them."

Wald's speech was printed in many newspapers and was featured in an issue of The New Yorker. He became an energetic advocate of what he called "survival politics," visiting college campuses and speaking on subjects including the Cold War, human rights and liberation movements.

His name came to appear on President Richard M. Nixon's enemies list.

Wald was born on the Lower East Side of New York City to parents who were working in the garment industry. He grew up in Brooklyn and graduated from what was then called Manual Training High School.

He received a bachelor's in zoology in 1927 from New York University's Washington Square College and earned a doctorate in 1932 from Columbia University. But his son Elijah said Sunday that the degree had never been officially awarded to him because he had never fulfilled the requirement of getting 200 copies of his doctoral thesis printed for distribution.

Wald did research on a National Research Council fellowship in Germany in 1932 and 1933, and that served as the foundation for his subsequent scientific work. But in 1933, the year Hitler came to power in Germany, Wald switched to the University of Chicago's department of physiology. He worked there in 1933 and 1934, then went to Harvard.

Other honors received by Wald include the Lasker Award of the American Public Health Association, the Rumford Medal of the American Academy of Arts and Sciences and the Eli Lilly Award of the American Chemical Society. He was also awarded a Guggenheim fellowship and numerous honorary degrees, and he was elected to the National Academy of Sciences and the American Philosophical Society.

His first marriage, in 1931 to Frances Kinsley, ended in divorce. In addition to his wife, Dr. Hubbard, Wald is survived by three sons, Michael, of Elmira, N.Y., David, of Monument Beach, Mass., and Elijah, of Somerville, Mass.; a daughter, Deborah, of San Francisco; nine grandchildren, and three great-grandchildren.

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