The elevated luteinizing hormone (LH) and androgen concentrations characteristic of women with polycystic ovaries (PCO) are considered crucial factors in their infertility. The somatostatin analogue octreotide lowers LH and androgen concentrations in women with PCO. The effects of octreotide given concurrently with human menopausal gonadotrophin (HMG) were therefore compared with that of HMG alone in 28 infertile women with PCO resistant to clomiphene. In 56 cycles of combined HMG and octreotide therapy there was more orderly follicular growth compared with the multiple follicular development observed in 29 cycles in which HMG was given alone (mean number of follicles > 15 mm diameter on the day of human chorionic gonadotrophin (HCG) administration: 2.5 +/- 0.2 and 3.6 +/- 0.4 respectively; P = 0.026). There was a significantly reduced number of cycles abandoned (> 4 follicles > 15 mm diameter on day of HCG) in patients treated with octreotide+HMG, so that HCG had to be withheld in only 5.4% of cycles compared to 24.1% with HMG alone (P < 0.05). The incidence of hyperstimulation was also lower on combined treatment. Octreotide therapy resulted in a more 'appropriate' hormonal milieu at the time of HCG injection, with lower LH, oestradiol, androstenedione and insulin concentrations. Although growth hormone concentration was similar on both regimens, significantly higher insulin growth factor-I concentrations were observed on the day of HCG in women on combined therapy than on HMG alone.