Antibodies to Chlamydia trachomatis (serum IgG antibodies with a titre of at least 32) were detected in 141 (86.0%) of 164 infertile women with tubal infertility (TF group) and in 20 (28.6%) in 70 infertile women with normal tubes (NTF group). The difference was highly significant (P less than 0.001), as was the difference in geometric mean titre of antibody-positive cases, 181 and 87, respectively. Pregnant, age-matched women were used as controls. Significantly fewer of these women (P less than 0.001) had antibodies, when compared with the TF group, 60 (36.6%) of 164, but not when the comparison was made with the NTF group, 31 (44.3%) of 70. There was a history of salpingitis in 64 (39.0%) of the 164 infertile women with damaged tubes. Neither the frequency nor the geometric mean titre of chlamydial antibodies differed between tubal factor infertility patients with and without a history of salpingitis. Previous chlamydial infection, reflected by serological markers, is strongly associated with tubal damage leading to tubal infertility. A large proportion of these cases run a silent course, since a majority of the antibody-positive patients with tubal infertility have never had salpingitis.