The objective of this study was to compare the efficacy and safety of a recombinant follicle stimulating hormone (FSH) preparation (Org 32489, Puregon) with a urinary FSH preparation (Metrodin) in infertile women undergoing in-vitro fertilization (IVF and embryo transfer and who were pituitary-suppressed with triptorelin. In an assessor-blind, group-comparative, multicentre study, 60 women were randomized to Org 32489 and 39 to urinary FSH. An evaluation of the main parameter, the mean total number of oocytes recovered, indicated a similar efficacy for the two preparations: 9.7 with Org 32489 versus 8.9 with urinary FSH. In addition, there were no significant between-group differences with respect to other efficacy variables such as the total dose used, the duration of the treatment, the number of follicles > or = 17 mm in diameter and embryo quality. The ongoing pregnancy rates per attempt (30.2 versus 17.4%) and per transfer (34.0 versus 18.8%) were higher with Org 32489, but this difference was not statistically significant. No clinically relevant differences between Org 32489 and urinary FSH were seen with respect to safety variables. Serum antibodies were not detected in any of the subjects. It is concluded that Org 32489 compares favourably with urinary FSH in the treatment of infertile pituitary-suppressed women undergoing IVF and embryo transfer.