Culture forms of 104 stocks of Trypanosoma cruzi isolated in different regions of the State of Bahia were compared by electrophoresis of six enzymes. The three distinct combinations of isoenzyme patterns seen were designated Zl, 22 and 23. In an area of endemic Chagas’s disease in eastern Bahia, T. cruzi Zl was associated with sylvatic mammals and sylvatic triatomines, whereas T. cruzi 22 was associated with a separate domestic cycle of transmission. T. cruzi Zl was also found in sylvatic triatomines from other parts of the State. In contrast, in an area of the SPo Francisco Valley region of western Bahia, both T. cruzi Zl and 22 were isolated from man, domestic animals, and peridomestic rats. T. cruzi 23 was isolated from an armadillo and from Panstrongylus geniculatus, a triatomine commonly found in armadillo burrows. Both T. cruzi Zl and 22 appeared to be pathogenic in man: T. cruzi Zl was isolated from patients with acute Chagas’s disease and from a single patient with chronic cardiac manifestations. T. cruzi 22 was isolated from some asymptomatic individuals but was also associated with acute disease and chronic cardiac and digestive syndromes.