In 265 Canadian women, with and without tubal factor infertility (TFI), we compared Chlamydia trachomatis cultures of endocervical swabs, endotubal swabs and biopsies, serology, and past history. A history of pelvic inflammatory disease (PID) was absent in 69.2% of TFI women, despite visual evidence of tubal damage. C. trachomatis was not isolated in any of 52 patients with TFI (TFI group), 114 having tubal ligation (STER group), or 99 patients having hysterectomy (HYST group). However, chlamydial antigen was detected with an immunochemical method in 1 of 16 tubal biopsy specimens from TFI women. The prevalence of chlamydial IgM or IgG antibody in serum was significantly higher (P less than 0.0001) in the TFI group (79.1%) than in the other two groups (relative odds, 6.3; 95% confidence interval: 2.5, 16.8). In seropositive (IgG or IgM) subjects, there was a significant (P = 0.003) and strong (relative odds, 5.1; 95% confidence interval: 1.5, 18.1) association between chlamydial IgA antibody and TFI. In women with TFI, there was no significant association between IgM or IgG seropositivity (P = 0.56). or IgA seropositivity (P = 0.53), and a negative history for PID. These findings are consistent with the hypothesis that C. trachomatis is a major cause of TFI following PID, which may or may not be asymptomatic.