The effect of growth hormone addition to human menopausal gonadotrophin (HMG), after pituitary down-regulation, on granulosa cell function, in in-vitro fertilization (IVF) was evaluated. Growth hormone or placebo were added in a prospective, randomized and double-blind manner to an existing IVF stimulation protocol. Forty-two normal ovulatory women (< or = 38 years old) with mechanical factor infertility and normal male factor were included in the study. Gonadotrophin-releasing hormone agonist (GnRHa) was given from day 21 of the previous cycle until human chorionic gonadotrophin (HCG) administration. Follicular stimulation with HMG was started after pituitary down-regulation. Growth hormone 12 IU/day or placebo were administered on alternate days, beginning day 1 until day 7 of HMG treatment. Granulosa cell function was evaluated, in all patients, by follicular fluid levels of ovarian steroids and insulin-like growth factor-I (IGF-I). In 14 patients, chosen arbitrarily granulosa lutein cells were cultured in the presence and absence of additional HCG. Follicular fluid levels of oestradiol, progesterone, testosterone and IGF-I were similar in both growth hormone and placebo groups. Basal and post-HCG levels of oestradiol and progesterone did not differ significantly between the two groups of granulosa lutein cell cultures. We conclude that after pituitary down-regulation, in-vivo administration of growth hormone with HMG in young ovulatory women does not seem to affect granulosa cell function when compared to the administration of HMG alone.