Kurt Julius Isselbacher (September 12, 1925 – July 18, 2019) was a German-born American physician and held the position of Mallinckrodt Distinguished Professor of Medicine at Harvard Medical School and director emeritus of the Massachusetts General Hospital Cancer Center.

After completing his residency in medicine at the Massachusetts General Hospital (MGH) in 1953, he became a clinical and research fellow at the National Institutes of Health (NIH).

He also held the position of the Mallinckrodt Distinguished Professor of Medicine at Harvard Medical School[3] and director emeritus of the Massachusetts General Hospital Cancer Center.

In addition, he elucidated the enzymatic mechanism for the formation of glucuronide conjugates, important for the detoxification of many compounds by the liver.

[3][8] Over the subsequent 30 years, his division became one of the leading centers of training, research and treatment of gastrointestinal diseases in the United States.

[3][8] His research during this period included the description and elucidation of a new hereditary disorder of leucine metabolism called isovaleric acidemia,[9] the definition of enzymatic defects in absorptive disorders, delineations of biochemical mechanism of nutrient absorption,[10] malabsorption,[11] and protein synthesis, derangements of metabolism and immunologic aspects of hepatic gastrointestinal diseases.

[8] Dr. Isselbacher trained over 140 clinical and research fellows both in gastroenterology and oncology and many of them have become leaders in their respective fields nationally and internationally.