Blood-group antigens are found on the surface of urothelial cells and may affect bacterial adherence and thereby the susceptibility to urinary tract infection. We determined the ABO, P, and Lewis blood-group phenotypes in 49 white women with histories of recurrent urinary tract infections and compared them with those found in 49 healthy control women without recurrent urinary tract infections. There was no significant difference between the two groups in the distribution of the ABO or P phenotypes. The distribution of Lewis blood-group phenotypes among control women was similar to that in the general population: secretor phenotype (Le(a-b+)), 74 percent; nonsecretor phenotype (Le(a+b-)), 18 percent; and recessive phenotype (Le(a-b-)), 8 percent. The following distribution was noted among the women with recurrent urinary tract infections: secretor phenotype, 45 percent; nonsecretor phenotype, 29 percent; and recessive phenotype, 26 percent (P = 0.002). When the women with nonsecretor and recessive phenotypes were combined and considered collectively, the odds ratio (an estimate of relative risk of recurrent urinary tract infection) for those without the secretor phenotype was 3.4 (95 percent confidence interval, 1.5 to 7.9). We conclude that there is an increased frequency of the Lewis blood-group nonsecretor (Le(a+b-] and recessive (Le(a-b-] phenotypes among women with recurrent urinary tract infections.