Dr. Robert J. Suhadolnik, 90, of Roslyn, a biochemist renowned for his research on AIDS and chronic fatigue syndrome, died Tuesday, Jan. 26, at Abington Memorial Hospital.

Through much of his career, Dr. Suhadolnik was a professor in the biochemistry department at Temple University School of Medicine, now the Lewis Katz School of Medicine. From a laboratory there, he and a half-dozen colleagues spent decades analyzing irregularities in immune-system pathways in patients with those conditions.

In the case of HIV, the researchers were seeking a treatment alternative for the infection, which typically mutates quickly and defeats the body's natural antiviral defenses. They developed a way to immunize against the spread of HIV through gene therapy, according to an account of the work in the Temple News. The therapy would replicate the target cells, with the introduced genes lying dormant until an infectious particle was encountered. They then would swing into action and produce antibodies to zap the infection.

"We have shown now that we can protect the cell from HIV infection in vitro, in the laboratory," Dr. Suhadolnik told the campus paper in 2007, when the team was awarded a $1 million grant by the National Institutes of Health for its ongoing work.

In patients with chronic fatigue syndrome, the researchers discovered a defective enzyme in their white blood cells. At one time, the ailment, which causes disabling exhaustion and flulike symptoms, was thought to be linked to depression and was considered a mental illness - a view superseded by the research of Dr. Suhadolnik and others.

"Something new is going on in chronic fatigue syndrome," Dr. Suhadolnik testified before Congress in May 1997. "RNASE L [an enzyme] was overactive, unlike anything we had ever seen before.

"We have had another surprise - we have seen a new form of RNase L, a smaller form of RNase L - in people with chronic fatigue syndrome.

"It is tempting to speculate that the presence and activity of the new form of RNase L correlates with the severity of clinical symptoms in people with [the disease]," he told the representatives.

Dr. Suhadolnik eventually patented a biological marker for chronic fatigue syndrome that was licensed through Temple to RED Laboratories of Belgium.

Temple honored him for his work with its Outstanding Research Award in 1990. He retired several years ago with the title of professor emeritus.

Dr. Suhadolnik was very popular with his colleagues, as much for the seriousness of his mission as for the example he set.

"No one worked harder or was more dedicated to his research than Dr. Suhadolnik," said Nancy Lee Reichenbach, an associate scientist who worked closely with him. "He had a thirst for knowledge that was unparalleled and made the most of every day. He had an almost photographic memory of the scientific literature."

He told his students that they were lucky to get paid to think, she said. He stressed attention to detail in the design and completion of all experiments.

"We were convinced that he wrote manuscripts in his sleep because he would arrive in the laboratory on a Monday morning with a nearly complete handwritten draft of a manuscript," Reichenbach said.

Born and reared in Forest City, Pa., Dr. Suhadolnik received his bachelor's degree in chemistry from Pennsylvania State University, his master's degree in chemistry from Iowa State University, and a doctorate in biochemistry from Penn State.

He maintained a cancer research lab at the Albert Einstein Medical Center from 1960 until he joined the Temple faculty in 1974. He had uninterrupted research grant support from 1961 to 2015 from the National Science Foundation and the National Institutes of Health.

He also published two books on biochemistry and made time to advise 20 Ph.D. candidates and mentor 26 postdoctoral fellows at Temple.

In private life, Dr. Suhadolnik was a dedicated parent and a skilled gardener.

"He was a fantastic father. He always made time for his children and grandchildren," said daughter Christine. "He never missed dinner. He always was there to check our homework and tuck us in."

He raised vegetables and fruit trees on the family's property in Roslyn, and his wife canned the produce. "It was like living on a farm," his daughter said. "It was an acre, and he used every bit of it."

Besides his daughter, he is survived by his wife, Dorothy R. Bezek Suhadolnik; daughters Michelle Baratta and Lorraine; eight grandchildren; two sisters; and a brother. A son, Robert, and a daughter, Andrea, died earlier.

Services were Tuesday, Feb. 2.

Donations may be made to the American Foundation for AIDS Research, 120 Wall St., 13th Floor, New York, N.Y. 10005; or the Chronic Fatigue Research Center, Stanford Genome Technology Center, 3165 Porter Dr., Palo Alto, Calif. 94304.

610-313-8102