A recent case of iatrogenic Cushing's syndrome and complete suppression of the pituitary-adrenal-axis in a patient with cystic fibrosis (CF) and allergic bronchopulmonary aspergillosis treated with itraconazole as an antifungal agent, and budesonide as an anti-inflammatory agent led to a systematic assessment of this axis and gonadal function in all patients treated with itraconazole in the authors' CF centre. Itraconazole can inhibit CYP3A, thus interfering with synthesis of gluco- and mineralocorticoids, androgens and oestradiol as well as the metabolism of budesonide. The aim of this study was to evaluate adrenal and gonadal function in patients treated with itraconazole with or without budesonide. An adrenocorticotrophic hormone (ACTH) test (250 microg tetracosactid) was performed in 25 CF patients treated with both itraconazole and budesonide, and in 12 patients treated with itraconazole alone (six patients with CF and six with chronic granulomateous disease). Mineralocorticoid and gonadal steroid function were evaluated by measurements of plasma-renin, follicle stimulating hormone, luteinising hormone, progesterone, oestradiol, testosterone, serum-inhibin A and B. ACTH tests performed as part of a pretransplantation programme in an additional 30 CF patients were used as controls. Eleven of the 25 patients treated with both itraconazole and budesonide had adrenal insufficiency. None of the patients on itraconazole therapy alone nor the control CF patients had a pathological ACTH test. Mineralocorticoid and gonadal insufficiency was not observed in any of the patients. Only one patient with an initial pathological ACTH-test subsequently normalised, the other 10 patients improved but had not achieved normalised adrenal function 2-10 months after itraconazole treatment had been discontinued. Suppression of the adrenal glucocorticoid synthesis was observed in 11 of 25 cystic fibrosis patients treated with both itraconazole and budesonide. The pathogenesis is most likely an itraconazole caused increase in systemic budesonide concentration through a reduced/inhibited metabolism leading to inhibition of adrenocorticotrophic hormone secretion along with a direct inhibition of steroidogenesis. In patients treated with this combination, screening for adrenal insufficiency at regular intervals is suggested.