Daniel Lee Gilbert, 75, an authority on oxygen poisoning and the harmful chemicals known as free radicals who at his death was an emeritus scientist at the National Institutes of Health, died Oct. 14 at Suburban Hospital after a stroke. He had pneumonia.

Dr. Gilbert, a Bethesda resident, worked from 1962 until retiring in June at the National Institute of Neurological Disorders and Stroke. He was chief of the reactive oxygen species unit in the biophysics section within the basic neurosciences program.

He was born in Brooklyn, N.Y., and served in the Army in Europe during World War II and participated in the Battle of the Bulge. His decorations included the Purple Heart.

He was a biology graduate of Drew University in New Jersey and received advanced degrees in physiology--a master's from the University of Iowa and a doctorate from the University of Rochester.

Dr. Gilbert taught physiology at Rochester, Albany (N.Y.) Medical College and Jefferson Medical College in Philadelphia before coming to the Washington area in 1962.

He contributed to many publications, including Science magazine, and helped edit numerous texts, including "Squid as Experimental Animals," published by Plenum Press in 1990.

Dr. Gilbert was the sole editor of "Oxygen and Living Processes: An Interdisciplinary Approach," published in 1981 by Springer-Verlag. This year, the New York Academy of Sciences published "Reactive Oxygen Species: From Radiation to Molecular Biology--a Festschrift in Honor of Daniel L. Gilbert."

He was a fellow of the American Association for the Advancement of Science and the Oxygen Society, which gave him its lifetime achievement award in 1998. He was a founder and past president of the Oxygen Club of Greater Washington and past president of the Washington Society for the History of Medicine.

A frequent speaker at seminars worldwide, he was a past Bowditch Lecturer of the American Physiological Society for outstanding scientists younger than 42.

Survivors include his wife of 36 years, Claire Gilbert of Bethesda; and a son, Raymond, of Indianapolis.