Dr. Benjamin Franklin Feingold, 81, an allergist and pediatrician who said hyperactivity in children often was caused by additives in their food, died Tuesday in the Kaiser Foundation Hospital. He had cancer.

He had been with Kaiser hospitals since 1951 and established Kaiser's allergy department. He was retired as head of the hospital's allergy department in January and was chief emeritus of the department when he died.

Dr. Feingold gained notice in 1973 when he told an American Medical Association meeting that some people, primarily children, became hyperactive through allergic reactions to certain synthetic additives and colorings in foods and that their conditions could be improved by following a diet devoid of the additives.

Hyperactivity, a disorder that causes individuals to be almost constantly active, has been treated with either stimulant drugs or tranquilizers with mixed success.

Dr. Feingold proposed that at least half of the children diagnosed as hyperatactive would be helped if they eliminated factory-produced soft drinks, cake, candy, pudding, processed cheeses and luncheon meats. He also said foods such as cucumbers, and many fruits, containing salicylates contributed to hyperactivity, as did tea, mint and wintergreen. He said treatment of hyperactive children with amphetamines was "doubtful therapy" and should be used only as last resort.

The "Feingold diet," a regimen that shunned food colorings, preservatives and artificial flavorings in foods, was the product of research that began in the 1960s after the allergist prescribed a change in food for an adult allergy patient at Kaiser. Dr. Feingold suspected a dietary link after a woman's condition improved and her psychiatrist noted that many of her psychological problems disappeared.

In 1975, Dr. Feingold's book, "Why Your Child is Hyperactive," drew sharp criticism from the food and drug industries. He also was the author of a 1979 book, "The Feingold Cookbook for Hyperactive Children."

His theories attracted numerous supporters and detractors in medical lay circles. But the theories around which debate swirled were based on Dr. Feingold's clinical observations in treatment of hyperactivity, not on controlled scientific experiments.

Dr. Feingold campaigned before the U.S. Food and Drug Administration for more labeling of food products. The FDA concluded on the basis of studies done in the late 1970s that the allergist's hypotheses were neither proved nor disproved.

In addition to criticism from the FDA and the food and drug industries, Dr. Feingold's theories received a mixed reception at the National Institutes of Health. A recent NIH conference concluded that while dietary treatment of hyperactivity "may be warranted," the Feingold diet "should not be universally applied." Studies at the University of Pittsburgh and University of Wisconsin also generally failed to support Dr. Feingold's findings.

Dr. Feingold was born in Pittsburgh and earned his undergraduate and medical degrees from the University of Pittsburgh. He was a fellow in pathology at the University of Gottingen, Germany, and was on the staff of the children's clinic at the University of Vienna in the late 1920s. He taught pediatrics at Northwestern University and was on the staff of hospitals in Los Angeles before joining the Kaiser Foundation Hospital.

Survivors include his wife and a stepson.