Various stimulation regimes have been tried to induce multiple follicular development for in-vitro fertilisation and embryo transfer. Human menopausal gonadotrophins have been widely used to induce follicular growth. To evaluate the role of the FSH: LH-ratio and the importance of LH concentrations, the results of a randomised assessor-blind group comparative efficacy and safety study are described. The effects of preparations, comprising FSH: LH-ratio of 3:1 and FSH: LH-ratio of 1:1 respectively, in stimulation of the ovaries for in-vitro fertilisation in infertile women are compared. Patients under 38 years of age with regular menstrual cycle (27 +/- 3 days and 32 +/- 3 days) are included. Sperm parameters have to be in normal range, according to WHO criteria. Follicular and luteal hormone parameters, ultrasound measurements, oocyte quality, fertilisation, cleavage and pregnancy rates are reported. The outcome of in-vitro fertilisation after the administration of preparations containing different ratios of FSH:LH leads to comparable results. However, the rate of ovarian hyperstimulation syndrome and the abortion rate after embryo transfer seems to be lower in patients stimulated with FSH dominant gonadotrophins.