One hundred and four Escherichia coli strains isolated in the Hospital Centre of Clermont-Ferrand (France) from faeces of 26 infants with diarrheal diseases and of 29 infants with non-diarrheal diseases were tested for their ability to adhere to intestinal villi of the human small intestine. The haemagglutination (HA) type (with human, bovine, chicken and guinea-pig erythrocytes) and the agglutination of adhering strains by anti-colonization factor antigen I (CFA/I) serum and by anti-CFA/II serum were determined. Seventeen strains adhered to the brush border of the human small intestine. All these strains were isolated from infants with diarrhea; among these strains, only two possessed one CFA: one of them exhibited HA type I and was agglutinated by the anti-CFA/I serum; the second exhibited HA type II and was agglutinated by the anti-CFA/II serum. Six strains exhibiting HA type III and nine exhibiting other HA types were not agglutinated by anti-CFA/I or CFA/II sera. There were no relationship between the adherence and the serotypes or the antibiotic resistance of these strains.