The genetic organization and epidemiology of Dr hemagglutinin was studied. Plasmids derived from pBJN406 and carrying transposon inserts were analyzed for their abilities to confer the mannose-resistant hemagglutination phenotype and expression of plasmid-encoded proteins. The 6.6-kilobase DNA fragment expressed five polypeptides with molecular masses of 15.5, 5, 18, 90, and 32 kilodaltons encoded by the draA, draB, draC, draD, and draE genes, respectively. Four genes, draA, draC, draD, and draE, were required for full mannose-resistant hemagglutination expression. Mutation in the draA gene, previously identified as encoding fimbrillin, resulted in loss of the adherence phenotype. We screened 658 strains isolated from patients with urinary tract infections (UTI) or from fecal samples for the presence of DNA sequences homologous to the draD gene. A significantly higher frequency of draD-related sequences was found among Escherichia coli strains from patients with cystitis than among strains from patients with other clinical forms of UTI. Association of draD-related sequences with O75 and other serotypes was observed. A possible role of Dr hemagglutinin as a virulence factor in lower UTI is discussed.