In earlier IVF programmes, subcutaneous buserelin (Suprefact, Hoechst) was initially administered three times per day (200 micrograms x 3); then twice daily (300 micrograms x 2). We now suggest that a single administration of 600 micrograms daily may be equally effective. In a preliminary study, 20 patients were selected on the basis of tubal or idiopathic infertility and received 0.6 ml buserelin subcutaneously once a day, beginning on day 1 or 2 of the cycle. A sufficient pituitary desensitization was obtained on day 10 in 75% of patients and on day 16 for 100% and the ongoing pregnancy rate was 35% per treatment cycle. A randomized study comparing the effect of 600 micrograms of buserelin administered in one (n = 50) or two injections (n = 46), has been carried out and indicates that the results in terms of the ovarian suppression and pregnancy rates, were similar. Therefore, this protocol represents a simplification of the treatment with buserelin.