In 51 patients, controlled ovarian hyperstimulation with clomiphene citrate (CC)/human menopausal gonadotropin (hMG), or hMG only, in 102 IVF cycles had previously resulted in a cancellation rate of 52% and no pregnancies. In 54 subsequent cycles the women were treated with prolonged administration of a gonadotropin-releasing hormone agonist (GnRHa) followed by hMG stimulation, the GnRHa group. The results were compared with the outcome of 47 cycles in patients who came for their first IVF attempt. In this group a CC/hMG regimen was used, the CC/hMG group. In the GnRHa group, 17 pregnancies were achieved, compared with 10 in the CC/hMG group. Only four cycles were cancelled in the GnRHa group, vis-à-vis 13 in the CC/hMG group, a significant difference. The study showed that prolonged use of GnRHa as a preparatory treatment is effective following previous failures of IVF.