On the basis of data from literature and by the use of commercial accessories radioimmunologic method of the determination od 17-alpha-hydroxiprogesteron (17-OHPG) serum level was determined in two variants: a) addition to the previous extraction, b) without extraction. It was initiated in the clinical work for diagnostic of congenital adrenal hyperplasia (CAH) induced by the enzymatic block of C21-hydroxilasis. 17-OHPG level was determined in a group of 15 children aged 2-12 of both sexes not suffering from endocrinous diseases. Mean values od X = 3.2 +/- 2.7 nmol/L and X = 4.3 +/- 3.3 nmol/L were obtained under a) and b), respectively. Also, 17-OHPG concentration was determined in 15 women without any endocrinous diseases by the method under b) and mean value of X = 2.5 +/- 1.7 nmol/L was obtained. 17-OHPG level was determined in a group of 7 children in whom CAH had been verified 3 days after the interruption of the substitutional therapy. According to the results of the investigation it was pointed out that there was a marked increase in 17-OHPG serum level (particularly by the use of b) method) which was far outside the range of reference values. In cases both with 17-OHPG determination and the daily pregnantriol excretion it was noticed that the increase in 17-OHPG was almost always accompanied by the increase in pregnantriol as well. Cortisolemia ranged from normal up to very lowered values.(ABSTRACT TRUNCATED AT 250 WORDS)