PROBLEM: To measure and compare concentrations of inhibin A, inhibin B, activin A and oestradiol in the follicular fluid of women with endometriosis, tubal damage and unexplained infertility with oocyte quality and fertilising capacity. Also, to assess whether impaired follicular function in women with endometriosis might be related to altered inhibin or activin concentrations and whether this correlated. METHOD OF STUDY: Follicular fluids were collected from individual follicles during oocyte retrieval for in vitro fertilisation (IVF) in natural cycles. Inhibin A, inhibin B and activin A were measured using two-site enzyme immunoassay, and oestradiol was assayed by fluoro-immunometric method. RESULTS: Follicular fluid inhibin A levels were found to be significantly higher in women with endometriosis. Inhibin A was directly correlated with follicle size. There was no correlation between the levels of inhibin A, inhibin B, activin A and oocyte quality or fertilising capacity in the three groups of women. CONCLUSIONS: Follicular fluid concentration of inhibin A is elevated in follicles of women with endometriosis and is positively correlated with follicle maturation. However, we were unable to demonstrate any association between the follicular fluid concentrations of inhibin A, inhibin B, activin A or oestradiol and the quality and fertilisation capacity of oocytes in women with tubal damage, unexplained infertility or endometriosis.