Editorial introduction to the paper by A. Castellani "Researches on the Etiology of Sleeping Sickness" reprinted from the Journal of Tropical Medicine, June 1, 1903.

The paper by Professor Aldo Castellani represents the first report suggesting the causative role of Trypanosoma spp. in the pathogenesis of sleeping sickness and confirms his pivotal role in solving the etiologic dilemma of the disease. Professor Castellani also contributed to a large extent to many other important microbiological discoveries, mainly in the field of mycology, protozoology and bacteriology.