Gonadotrophin-releasing hormone (GnRH) analogues improve the outcome of treatment with IVF by increasing the number and quality of oocytes retrieved and by reducing cycle cancellation rates. Whilst short-acting GnRH analogues are most commonly used, depot preparations are now available that are more convenient for patient use. Some studies have reported that pregnancy rates with depot GnRH analogues are similar to those of short-acting preparations, but others have suggested that the more profound down-regulation seen with depot GnRH analogues results in inferior embryo quality. The purpose of this study was to determine whether a lower than conventional dose of a depot GnRH analogue may be more appropriate for use in ovarian stimulation prior to IVF. Sixty patients were randomized to receive either 3.75 mg (conventional dose) or 1.87 mg (low dose) triptorelin prior to ovarian stimulation for IVF. Suppression was measured using serum concentrations of LH measured 2 and 3 weeks after the administration of the GnRH analogues, the dose of gonadotrophin used and the time to resumption of menses. Mean concentrations of LH were 2.2 +/- 1.0 and 1.1 +/- 0.6 IU/l in the conventional dose group and 3.5 +/- 5.5 and 2.7 +/- 1.9 IU/l in the low dose group (P < 0.05 at 2 and 3 weeks). There were no significant differences between the doses of gonadotrophins used, the number of oocytes and embryos available and the time to resumption of menses, nor in the pregnancy rates. Although the degree of suppression as measured biochemically was more profound with the conventional dose, this did not affect the IVF outcome. The use of a lower dose therefore appears to be equally effective and could contribute to a reduction in the cost of treatment.