LHRH agonists are being increasingly used in ovulation stimulation protocols in IVF programmes. We have compared the results of two methods of utilization of LHRH agonists. In the long protocol, gonadotrophin stimulation was only commenced after a preliminary period of pituitary desensitization with LHRH agonist. In the short protocol, exogenous gonadotrophins were administered shortly after the start of LHRH agonist therapy, benefiting from the gonadotrophin flare-up effect. One-hundred-and-eighty-six patients were divided equally between the two treatments. There was no difference in the ovarian response on the day of HCG or the number of mature oocytes recovered. The cleavage rate of mature oocytes was higher in the short protocol (70, versus 56, P less than 0.01). The ongoing pregnancy rate per treatment cycle was similar in both groups (18, in the long protocol and 16, in the short protocol). Analysis of the luteal phases revealed a trend for higher progesterone values in the long protocol although this was only significant on the second day following oocyte retrieval. As the clinical results were similar other factors should be taken into account when deciding therapy. These include patient convenience, cost and side-effects. Other schedules of ovulation stimulation using LHRH agonists are discussed.