BACKGROUND The study explores the relationship between serum chlamydia antibody titres (CATs) and detection of tubal damage in infertile women. METHODS The tubal status and pelvic findings in 1006 women undergoing laparoscopy for infertility were related to CAT, which was measured using the whole-cell inclusion immunofluorescence test. RESULTS A negative correlation between CAT and age was noted. A linear trend between serum CAT and the likelihood of tubal damage, including severe damage, was observed (P < 0.001). Titres in women with tubal damage (median 1:1024; range <1:64-1:4096) were significantly (P < 0.001) higher than in women with endometriosis alone (median <1:64; range <1:64-1:512) or those with a normal pelvis (median <1:64; range <1:64-1:1024). Women with positive titres were more likely to have pelvic adhesions than tubal occlusion unless titres were very high, when tubal damage was likely to be more severe. CONCLUSIONS CATs are of predictive value in the detection of tubal damage and are quantitatively related to the severity of damage. For practical clinical purposes, Chlamydia serology is useful mainly as a screening test for the likelihood of tubal damage in infertile women and may facilitate decisions on which women should proceed with further investigations without delay.