Trypanosoma (Schizotrypanum) species isolated from bats (Microchiroptera) in Europe and Latin America were examined by determining the buoyant densities of their nuclear and kinetoplastic deoxyribonucleic acid (DNA) and the electrophoretic patterns of six isoenzymes. By these criteria they were separated into three distinct groups—two from Europe (T. dionisii and T. vespertilionis) and one from America. T. dionisii was also separable by its morphology in vitro. Geographical location and DNA buoyant densities suggested that the American stocks were more closely related to T. cruzi than to the European species, though they differed from it marginally in kinetoplastic DNA density and in being non-infective to mice. Similar stocks studied by other workers have been shown to differ from T. cruzi also in reduced infectivity to, and lack of natural association with, Triatominae, and in antigenic composition. It is therefore proposed that trypanosomes of the subgenus Schizotrypanum occurring naturally in Microchiroptera and differing from T. cruzi sensu stricto as outlined above should be treated as a distinct subspecies, T. cruzi marinkellei ssp. nov. T. cruzi sensu stricto thus becomes the nominate subspecies T. cruzi cruzi Chagas 1909.