Several growth factors augment the ovarian response to gonadotrophins and growth hormone is known to regulate the production of insulin-like growth factor-1. With this in mind, 20 women who had previously responded sub-optimally to standard ovarian stimulation regimens for in-vitro fertilization and embryo transfer (IVF-ET) were recruited into a randomized trial to study the effect of co-treatment with growth hormone (Norditropin, Novo Nordisk Gentofte A/S). Intramuscular injections of growth hormone (24 IU) or placebo were given on alternate days concurrently with the same daily dosage of gonadotrophin as administered in the patient's pretreatment cycle. Overall, there was no improvement in the ovarian response to the growth hormone-augmented regimen of stimulation although there was a tendency for the development of more follicles (P = 0.06). When the results from the patients with ultrasound-diagnosed polycystic ovaries were analysed separately, however, more follicles developed (P = 0.04), more oocytes were collected (P = 0.03) and there was a trend towards higher urinary oestrogen production following growth hormone therapy. There was no improvement in the ovarian response in patients with normal ovaries. The treatment was not associated with any adverse effects. We conclude, therefore, that in a subgroup of patients who respond sub-optimally to standard ovarian stimulation regimens for IVF-ET and who have ultrasound-diagnosed polycystic ovaries, systemic growth hormone is an effective adjunctive therapy.