Fimbriae from three Escherichia coli strains, C1212, C1214, and C1023, isolated from urinary tract infections, have been purified and characterized by determination of the N-terminal sequences, amino acid composition, and molecular weights of their respective subunits. Furthermore, their immunological interrelationships have been investigated. The three strains all harbored more than one fimbrial species each. Immunologically different type 1-like fimbriae, termed 1A, 1B, and 1C, with highly homologous N-terminal sequences were isolated, of which strain C1212 possessed 1A and 1C, strain C1214 possessed 1A and 1B, and strain C1023 possessed 1A and 1C. Type 1A is known to cause a mannose-sensitive hemagglutination similar to that described for type 1 fimbriae, whereas the functions of types 1B and 1C are not yet known. Strain C1212, in addition, harbored the F7 fimbrial antigen which causes mannose-resistant hemagglutination and adherence to urinary epithelial cells. The N-terminal structure of this antigen seems to indicate a possible evolutionary kinship to the type 1-like fimbriae, although they are immunologically unrelated. Our results indicate that fimbriation of pathogenic wild-type strains can be of an intricate variety.