The purpose of the study was to determine whether serologic studies for Chlamydia would be helpful in identifying cases in which a tubal factor is responsible for infertility. One hundred and fourteen infertile women, consecutive patients who came to the infertility clinic at the University of Texas Medical Branch at Galveston, had serological tests for Chlamydia and subsequent tubal evaluations by laparoscopy or laparotomy. Seventy-four patients (65%) had positive titers for Chlamydia, of whom 57 (77%) were found to have tubal obstruction. Forty-four had distal tubal obstruction; three had cornual obstruction; and ten had peritubal adhesions. Of the 40 patients with negative titers for Chlamydia, only 14 (35%) were found to have tubal obstruction. The difference in the incidence of tubal disease between women with positive titers and those with negative titers was statistically significant (P less than .002). A significant correlation (P less than .001) was observed between the prevalence of antibodies and distal tubal obstruction. Of the 74 patients with positive titers, 48 (65%) had no history of prior symptomatic pelvic inflammatory disease. These findings suggest that chlamydial infection, as evidenced by positive antibody titers, is associated with a significantly high incidence of tubal infertility and that in the majority of these patients, the prior infection was subclinical and asymptomatic.