The authors divided forty children and adolescents with inborn adrenal hyperplasia caused by a block of 21-hydroxylase of steroids (CAH) according to clinical criteria into adequately and inadequately treated. Substitution treatment with hydrocortisone or hydrocortisone combined with fludrocortisone was administered three times a day in individual doses. In order to find an adequate indicator of the adequacy of therapy, the authors assessed in addition to total urinary 17-oxosteroids also 17 alpha-hydroxyprogesterone, androstenedione and 11 beta-hydroxyandrostenedione in serum. The values of urinary 17-oxosteroids did not correspond to the clinical condition of the children; in younger children three was a high percentage of falsely positive and in older children of falsely negative results. As to serum steroids, the most suitable indicator for monitoring was 17-hydroxyprogesterone. The authors consider its levels above 30 nmol/l as a basis for consideration of raising therapeutic doses, while levels below 2.2 nmol/l signalize possible overdosage of the drug. Concurrently elevated levels of 17-hydroxyprogesterone and androstenedione are found in particularly inadequately treated children. 11 beta-hydroxyandrostenedione is not a useful indicator for monitoring of CAH treatment. In any case it is necessary, when controlling CAH therapy, to select an individual procedure and to evaluate results in the context with the patient's clinical condition.