In 33 patients treated with a combination of an LHRH agonist (LHRH-A) and gonadotrophin in a long protocol, a biological hyperstimulation occurred (E2 greater than 2500 pg/ml on the day of HCG administration and 4722 +/- 1190 pg/ml the day after, with greater than 10 follicles greater than 12 mm on each ovary). The replacement of fresh embryos were deferred and LHRH-A was continued, and an endometrial biopsy was performed on the theoretical day of replacement (2 days after oocyte recovery). With this technique, we obtained a mean number of 17.9 +/- 7 oocytes, a fertilization rate of 49% and a replacement rate of 87% in a deferred cycles. The overall pregnancy rate of frozen-thawed embryos was 27% in the seven spontaneous cycles, 12 induced cycles and 10 artificial cycles. Only one severe hyperstimulation occurred and this case emphasizes that caution remains necessary even with this technique.