This study assessed the effects on plasma adrenocorticotrophic hormone (ACTH) and cortisol concentrations of 3 months' treatment with intranasal nafarelin 200 micrograms b.d. in 11 women (aged 26-43 years) for the treatment of endometriosis (n = 9), fibroids (n = 1) and pre-menstrual syndrome (n = 1). Serial blood samples were taken over 5 h, before and after nafarelin administration on the first day of treatment, and after 1 and 3 months' treatment. Control samples were taken before and after intranasal placebo administration on the day before nafarelin was commenced. The area under the curve (AUC) for mean ACTH concentrations at each time point from 0 to 240 min was calculated. There were no statistically significant changes in total secretion of either ACTH or cortisol. There was a transient rise in ACTH 30-60 min after nafarelin administration on the first day of treatment in seven out of 11 women. The rise did not exceed the normal range. Seven women with ovarian suppression (oestradiol concentration < 175 pmol/l by day 28) had consistently lower mean ACTH concentrations at all time points than the four remaining women who had oestradiol concentrations 222-880 pmol/l by day 28. Cortisol concentrations were unaffected by nafarelin. We conclude from the results of this study that 3 months' treatment with nafarelin has no effects on adrenal function, as assessed by ACTH and cortisol concentrations.