The study was undertaken to examine any differences existing in total cortisol concentrations in the follicular fluid (FF) of pre-ruptured follicles between 'low responder' patients (group 1, n = 20) and 'good responder' patients (group 2, n = 15). The groups were defined according to how many oocytes had been retrieved during the previous in-vitro fertilization procedure (group 1: three or fewer; group 2: more than three) and total oestradiol concentration at previous in-vitro fertilization (IVF) (group 1: < or = 500 pg/ml; group 2: > 500 pg/ml). All patients were aged 36-43 years (group 1 mean +/- SD: 38.2 +/- 4.7; group 2: 32.1 +/- 3.8 years) and were diagnosed with tubal or unexplained infertility. The total FF cortisol concentrations obtained in conjunction with an IVF procedure were assayed and related to oocyte fertilization. Follicular fluid was analysed for total cortisol content. Only follicles between 19 and 20 mm diameter were analysed in both groups. After aspiration of blood-free FF, total cortisol concentrations were measured by radioimmunoassay, designed for the quantitative measurement of cortisol, and related to oocyte fertilization. Total cortisol concentration in FF from fertilized oocytes was 9.7 +/- 0.6 microg/ml (mean +/- SD) in group 1 compared to 9.2 +/- 4.4 microg/ml in group 2 (not statistically significant). Total cortisol concentrations were not associated with oocyte fertilization and no difference between the groups was found in total cortisol concentrations in the FF of unfertilized oocytes or empty follicles.