One-hundred-and-twelve samples of follicular fluid from 32 patients undergoing in-vitro fertilization and embryo transfer were analysed in this study. The follicular fluids were analysed for any relationships between oestradiol, progesterone and 17-alpha-hydroxyprogesterone levels, the progesterone/oestradiol and 17-alpha-hydroxyprogesterone/oestradiol ratios and oocyte maturity and fertilization rates. In Group A, consisting of women who used analogues of gonadotrophin-releasing hormone during ovarian stimulation with human menopausal gonadotrophin, the progesterone/oestradiol ratio rose in parallel with the fertilization rate (P < 0.05). Group B comprised patients treated with human menopausal gonadotrophin alone. No significant relationship was found between the other parameters, oocyte maturation and fertilization rates in either group.