Ten endocrinologically normal women were injected subcutaneously with 500 micrograms D-Ser(TBU)6-EA10-LHRH (buserelin) on days 3,4 and 5 after the start of the menses. Two types of response were observed. Five women (group A) responded promptly and had a mean number of 13.4 oocytes retreived after 11.4 days of stimulation. In the second group (B), two to three times more HMG was needed to obtain a mean number of 7.3 oocytes after 17.2 days of stimulation. The response upon stimulation could be predicted by the serum gonadotrophin output on days 4 and 5 of the cycle. One woman from group B had a premature LH rise on day 16 and luteinization; her cycle was abandoned. In the four other patients of group B, serum and urinary LH concentrations showed that pituitary gonadotrophin secretion had recovered before the ovulatory stimulus, without signs of premature luteinization. Two women in each group became pregnant, one of whom aborted. This short-term GnRH agonist treatment could be an alternative method for ovarian stimulation, although it did not totally prevent the occurrence of an endogenous LH surge.