In this study the parameters of normal ovarian cycles were prospectively applied in a programme of ovulation induction with human menopausal gonadotrophin (HMG) and human chorionic gonadotrophin (HCG). Hypo-oestrogenism and failure of clomiphene administration were the main indications for treating 42 patients during 128 cycles with gonadotrophins. The initial HMG dosage was 1 ampoule per day. The dosage was adjusted daily in accordance with serum oestradiol response and ultrasound findings. HCG was administered under the following conditions: average follicle size of at least 18 mm, not more than 2 follicles present, optimal cervical mucus, and serum oestradiol levels between 1 000 and 3 000 pmol/l. Ovulation was successfully induced in 90% of treated cycles and 20 pregnancies ensued. If anovulatory patients with additional causes for infertility were excluded, the pregnancy rate per treated cycle was 30%. Two twin pregnancies developed and no cases of clinical ovarian hyperstimulation syndrome occurred. The maximum follicle size and cervical mucus score did not differ significantly from these parameters in spontaneous ovulatory cycles. Preovulatory serum oestradiol levels and mid-luteal progesterone levels, however, were significantly higher in the gonadotrophin-stimulated cycles.