Non-classic congenital adrenal hyperplasia (NCAH) is a rare cause of hirsutism and it results from a defect in the biosynthetic pathway of cortisol and/or aldosterone. 250 mug ACTH test (SDT) is used in the diagnosis of this disease. Our aim was to investigate the responses of 11-deoxycortisol to 1mug ACTH (LDT) test in women with 'NCAH due to 11-beta hydroxylase (11-beta OH) deficiency and to compare them with the values obtained after SDT in the patients and in the control subjects. Eleven patients with NCAH due to 11-beta OH deficiency and '15 control subjects were involved in the study. The main complaint of the patients with NCAH was hirsutism and the diagnosis was made if the adrenal 11-deoxycortisol response to SDT exceed threefold the 95th percentile of controls. ACTH stimulation tests were carried out consecutively by using 250 mug and 1 mug intravenous ACTH as a bolus injection after an overnight fast, and blood samples were drawn at 0,30 and 60 min. Peak cortisol, 17-hydroxyprogesterone (17-OHP) and DHEAS responses were similar in LOT and SDT while 11-deoxycortisol responses to LDT (15.7 +/- 1.8 nmol/L) were significantly (p < 0.005) lower than the results obtained after SDT (76.3 &PLUSMN; 21.4 nmol/L) in women with 11-β OH deficiency. Peak cortisol and 17-OHP responses to LDT in patients and control subjects were similar. Peak 11-deoxycortisol responses to LDT were significantly (p<0.05) higher in NCAH patients (15.7 +/- 1.8 nmol/L) than in the control subjects (6.5 +/- 0.8 nmol/L). However, in LDT, all patients had peak 11-deoxycortisol level lower than threefold the 95th percentile (25.8 nmol/L) of controls. This study represents the first demonstration that LDT gives similar cortisol but not 11-deoxycortisol responses to SDT in patients with 11-beta OH deficiency. This study also showed that LDT can not replace SDT in every clinical situation.