The prevalence of IgG antibodies to C. trachomatis was determined in 185 infertile women who underwent laparoscopy, and 110 pregnant women with no known infertility problems. In addition, chlamydial antigens were evaluated by EIA in cervical samples taken from all subjects. Subjects with tubal infertility had the highest prevalence of chlamydial antigen and antibody (P less than 0.01). While the percentage of subjects with antigen and antibody positive was 11.6 per cent, those with antigen negative and antibody positive averaged 55.8 per cent among women with tubal related infertility. The results of our study provide additional support to the concept that infertility of tubal etiology often is a sequela of a previous chlamydial infection.