GH synthesis and secretion are influenced by several factors, including age, body weight, and sex steroid hormones. Endogenous and exogenous estrogens influence the circulating levels of GH. The purpose of the present investigation was to define the relationship between serum GH and estradiol levels during the follicular phase in women with normal ovulatory menstrual cycles compared with that in women undergoing superovulation with human menopausal gonadotropins (hMG) alone or hMG plus GnRH agonists during treatment for infertility. Serum GH and estradiol levels were determined by immunoassay in eight women during the follicular phase of a spontaneous natural cycle (group I). Thirty women underwent ovulation induction with hMG alone (group II), and 30 women received GnRH agonists followed by hMG (group III). During the follicular phase estradiol levels increased gradually in group I and reached a peak estradiol level of 1.19 +/- 0.2 nmol/L (mean +/- SEM). As expected, estradiol levels rose faster and reached higher levels in groups II and III (5.44 +/- 0.62 and 8.73 +/- 0.91 nmol/L, respectively). Whereas serum GH levels increased minimally in group I, reaching a peak level of 2.54 +/- 1.15 nmol/L, serum GH concentrations increased markedly after day 8 in groups II and III, reaching peak levels of 8.70 +/- 1.58 and 7.54 +/- 1.12 nmol/L, respectively (P less than 0.01). Basal to peak GH levels were higher in groups II and III than in group I. In summary, there are modest increases in GH levels during the follicular phase of the normal menstrual cycle, but the levels are markedly increased during superovulation with hMG or hMG plus GnRH agonists, and parallel increases in estradiol levels.