Rapid radioimmune assaying of LH [luteinizing hormone] was carried out 4 times daily on 52 women in the preovulatory phase of the cycle. This method enables the precise detection of the LH surge and recovery of the mature oocyte by laparoscopic aspiration of the follicular content, just before ovulation, which is between 28 and 36 h after the start of the LH surge. The oocyte was recovered in 27 of 41 patients with a normal cycle (66%). The rate of recovery per aspirated follicle is comparable in a natural cycle to that after treatment with Clomid (80-84%).