Steroid synthesis inhibitors are commonly used in the treatment of patients with Cushing's disease, but may also improve psychopathology in hypercortisolemic depressed patients. Since glucocorticoids exert a negative feedback at pituitary and supra-pituitary levels, the inhibition of steroid synthesis may lead to increased expression of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP). We studied the effect of treatment with 800 mg ketoconazole (3 weeks) upon the concentrations of basal plasma cortisol in the evening, corticosteroid-binding globulin (CBG), dehydroepiandrosterone-sulfate (DHEA-S), and ACTH as well as the concentrations of cortisol, CRH, and AVP in cerebrospinal fluid (CSF) at 8.30 h in 10 healthy, male volunteers. While we found cortisol plasma concentrations to be unchanged, we noted a significant increase in ACTH (post: 45.1 ± 43.5; pre: 14.2 ± 5.2 pmol/l; F1,8 = 9.78, p<0.02) and CBG concentrations (post: 38.8 ± 4.3; pre: 31.9 ± 4.2 mg/l), but DHEA-S plasma concentrations declined (post: 1.75 ± 1.83; pre: 2.75 ± 2.80 mg/l; F1,8 = 7.9, p<0.03). CRH concentrations in CSF were unchanged after treatment (post: 62.5 ± 15.9; pre: 63.7 ± 13.9 pg/ml), while there was a trend for AVP concentrations to rise during treatment (post: 2.52 ± 1.18; pre: 1.92 ± 0.96 pg/ml; paired t = -1.9, p<0.1). Cortisol CSF concentrations declined in the elderly (pre: 52.5 ± 23.2; post: 26.7 ± 4.6 nmol/l), but not in the young subgroup (pre: 15.6 ± 11.3; post: 27.7 ± 9.4 nmol/l). We thus conclude that the treatment of healthy controls with steroid synthesis inhibitors does not lead to a major increase in CRH secretion.