Three hundred and twenty-seven consecutive in-vitro fertilization (IVF) cycles in which luteal-phase leuprolide had been given were ranked according to the number of pre-ovulatory oocytes obtained (1-5, 6-10, greater than 10). Excess pre-embryos were cryopreserved at the pronuclear stage and later transferred into monitored natural cycles on the day after ovulation. The results indicate that the retrieval of large numbers of pre-ovulatory oocytes (greater than 10) has a small negative impact on oocyte quality as judged by fertilization rates (4% lower). However, implantation was not impaired compared to lower levels of retrieval in either the original IVF or subsequent cryo-thaw cycles. Overall, despite the small reduction in fertilization rate, the retrieval of many pre-ovulatory oocytes has produced a 'take-home baby rate' per stimulation cycle of 28.3% when 6-10 pre-ovulatory oocytes were retrieved and 41.5% when greater than 10 were retrieved: even higher rates are anticipated when the remaining cryopreserved pre-embryos are ultimately thawed.