Levels of immunoglobulin G (IgG) antibodies to Chlamydia trachomatis and Neisseria gonorrhoeae were determined by enzyme-linked immunosorbent assay (ELISA) in 37 infertile Gambian women with bilateral fallopian tube occlusion and in 37 pregnant controls matched for age, ethnic group, and domicile. The infertile women had a significantly higher prevalence of antibodies to C. trachomatis serotype L1 (P = 0.01) and to purified N. gonorrhoeae pili, outer membrane, and lipopolysaccharide antigens (P < 0.01 in each case). Serological studies of immunoglobulin A (IgA) antibodies to C. trachomatis were less sensitive than the IgG studies in discriminating between the pregnant and infertile groups, suggesting that much of the infertility due to chlamydiae was the result of past rather than current infection. The data suggest that both C. trachomatis and N. gonorrhoeae are important causes of infertility due to tubal pathology in Gambian women.