A case-control study was performed on 94 women with acute salpingitis and 12 women with salpingitis and perihepatitis; all patients included in the study were infected with Chlamydia trachomatis, and all had been subjected to diagnostic laparoscopy. None of the 12 patients with, but 38 (40%) of the 94 patients without, perihepatitis used oral contraceptives (P = 0.002). The geometric mean titre of serum IgG antibodies to C. trachomatis was higher among patients with (1:1021) than among patients without (1:69) perihepatitis (P = 0.0001). Oral contraceptive users had lower geometric mean titre of antibodies to the organism (1:25) than non-users (1:109, P = 0.001). The study suggests that oral contraceptive use may modify the clinical manifestations of chlamydial pelvic inflammatory disease.