To examine the gonadotropic milieu presiding over recruitment and selection of a dominant follicle during gonadotropin induction of ovulation, four patients were studied over nine cycles of human pituitary gonadotropin (hPG) therapy. These hypogonadotropic subjects received a routine schedule of hPG injections monitored by daily urinary estrogen and pregnanediol determinations. Serum FSH, LH, and PRL profiles were measured in daily morning blood samples throughout each menstrual cycle. hPG therapy produced markedly abnormal gonadotropin patterns. Mean serum FSH levels were above the upper limit of the normal serum FSH range and no early or midfollicular FSH peaks occurred. The FSH-LH ratio was abnormally high for 8 days before ovulation. Progressive and marked elevations of serum PRL developed during hPG treatment. A bimodal luteal phase serum PRL profile appeared with peak values of 40.7 +/- 5.6 ng/ml (mean +/- SE) 1 day and 42.0 +/- 3.0 ng/ml 9 days after the LH peak. We conclude that: 1) Current gonadotropin treatment regimens to induce ovulation produce radioimmunoassayable serum FSH, LH, and PRL profiles which are qualitatively and quantitatively abnormal, and 2) Excessive FSH levels and the elevated FSH-LH ratio orchestrate aberrant folliculogenesis and result in the clinical problems of multiple ovulation and hyperstimulation.