['To establish whether time to down-regulation and pregnancy and live birth rates were different when buserelin acetate was started in the midluteal phase or early follicular phase in IVF-ET patients.', 'Prospective, controlled, randomized, parallel-group multicenter clinical study.', 'Women attending seven infertility clinics.', 'One hundred twenty-four women with tubal or unexplained infertility with normal menstruation and fertile partners.', 'Intranasal buserelin acetate started in the midluteal or early follicular phase combined with standard hMG and hCG stimulation after achievement of down-regulation. Established IVF-ET methods.', 'Duration of down-regulation; clinical pregnancy and live birth rates.', 'Kaplan-Meier estimations of the duration of down-regulation were 15.5 days when buserelin acetate was started in the early follicular phase (127 cycles) and 14.6 days when it was started in the midluteal phase (96 cycles). This difference was statistically significant. The pregnancy rates per first treatment cycle, treatment cycle, oocyte retrieval, and ET were significantly higher when buserelin acetate was started in the midluteal phase. The live birth rates were also higher, but only significantly so for the rate per first treatment cycle.'] Is midluteal buserelin superior to early follicular phase buserelin in combined gonadotropin-releasing hormone analog and gonadotropin stimulation in in vitro fertilization?