In total, 50 couples participated in a pilot study evaluating the efficacy of various regimens of gonadotrophin-releasing hormone agonist (GnRHa) in association with recombinant human follicle-stimulating hormone (recFSH) in women undergoing in-vitro fertilization (IVF) and embryo transfer. The women were treated with recFSH alone (group I), or with recFSH in conjunction with pituitary desensitization using a buserelin intranasal spray, 4 x 150 micrograms per day, in a short protocol (group II) or in a long protocol (group III), or using triptorelin in a long protocol, giving a single dose of 3.75 mg i.m. (group IV) or daily s.c. injections of 200 micrograms (group V). In all women, treatment with recFSH resulted in multiple follicular growth and rises of serum inhibin and oestradiol. The latter indicates that the amount of remaining luteinizing hormone (LH) was sufficient to support FSH-induced oestrogen biosynthesis. On the day of human chorionic gonadotrophin (HCG) administration, endogenous LH was most profoundly suppressed in subjects treated with triptorelin. The median number of ampoules and treatment days required in the various treatment groups varied from 21 to 36 ampoules and from 7 to 14 days, respectively. The median number of oocytes per group ranged from 9 to 11 and all cumulus-corona-oocyte complexes, with the exception of two, were classified as mature. The median fertilization and cleavage rates ranged between the treatment groups from 40 to 73% and from 73 to 100%, respectively. Fertilization failure of retrieved oocytes occurred in six couples with andrological or unexplained infertility. One patient had no transfer because of insufficient embryo quality.(ABSTRACT TRUNCATED AT 250 WORDS)