To evaluate the effects of synthetic growth hormone-releasing factor (GRF) in women with idiopathic infertility who were treated with human menopausal gonadotrophin (HMG), 13 women with this condition were randomly assigned to undergo treatment with HMG-GRF (500 micrograms twice daily) or HMG-placebo. Conception occurred in four of six women (14 cycles) who received HMG-GRF and in one of seven women (22 cycles) who received HMG-placebo. No difference was found in the amount of HMG and the duration of HMG required to induce ovulation between the two groups of patients. The overall serum growth hormone and insulin-like growth factor I concentrations were higher in the GRF than in the placebo group. No difference was found in serum oestradiol or inhibin concentrations between the two groups. Our results suggest that in women with idiopathic infertility, administration of GRF does not decrease the duration or the amount of HMG required to induce ovulation. However, it appears that in this small group concomitant treatment with GRF increases the pregnancy rates in women who are treated with HMG (4/14 cycles compared with 1/22 cycles).