Fecal samples collected from 237 diarrheic infants in Kampala, Uganda and from 159 healthy cattle from a ranch in the Central Region of Uganda were investigated for the presence of Escherichia coli O157 and other types of Shiga toxin-producing E. coli (STEC). E. coli O157 were not detected in 150 stool samples from children which were cultivated on sorbitol MacConkey agar. A search for all types of STEC performed on 87 additional human stool samples with an enzyme-immunoassay for Shiga toxins (Premier EHEC) was also negative. Forty-two stool samples from infants were additionally investigated for enteropathogenic E. coli (EPEC) by DNA-hybridization with an eae-specific gene probe. Compared to STEC, EPEC were frequent and found in six (14.3%) of these 42 randomly selected stool specimens. We were further interested in the role of cattle as a reservoir for STEC in Uganda. STEC were isolated from 45 of 159 cattle from a herd in the Central Region of Uganda. STEC strains from cattle belonged to 16 different O- and nine different H-types and nine O:H types were identical to those found in bovine STEC from other continents. Only one bovine STEC strain was positive for the eae-gene, and O-groups associated with enterohemorrhagic E. coli (EHEC) types (O26, O103, O111, O145 and O157) were not found. Our report demonstrates that STEC are not frequent in urban children in Uganda, but domestic cattle were identified as an important natural reservoir for these organisms in this country.