Long-acting GnRH-a (D-Trp6 microcapsules, 3.2 mg) was intramuscularly injected, either in early follicular phase (group A) or midluteal phase (group B). Two hundred sixteen cycles were randomly allocated. Ovarian suppression was significantly more prompt in group B. Follicle cysts were diagnosed in 19% and 16% of groups A and B, respectively; their appearance and regression were significantly more rapid in group B cycles. More ampules of human menopausal gonadotropin were needed in group B. The number of oocytes retrieved was not significantly different between the groups. However, in group A more mature oocytes and more embryos with good morphology were achieved in the patients. Cancellation rate was 2.8% in groups A and B. Pregnancy rate and outcome were similar in both groups.