Naunyn produced a classic monograph on gall-stones, devising an accurate chemical classification. He was one of Frerichs’s best pupils and became Professor of Clinical Medicine successively at Dorpat, Berne, Königsberg, and Strasburg. English translation, London, 1896.

Naunyn devoted his life to the study of metabolism in diabetes and in diseases of the liver and pancreas. This is his most significant work. He was a co-founder of the Archiv für experimentelle Pathologie.