Serum 170H‐progesterone estimations in the diagnosis and management of congenital adrenal hyperplasia. The results of serum 170H‐progesterone estimations performed during a 12 month period on 9 children with congenital adrenal hyperplasia due to deficiency of 21 hydroxylase are reviewed and correlated with measurements of urinary 17‐oxosteroids, pregnanetriol and 11‐oxygenation index. It is concluded that this investigation is not reliable as a sole index of control but is useful in the diagnosis of congenital adrenal hyperplasia and in its management when used in conjunction with the traditional controls. It is of no use in indicating overtreatment. Difficulties in the interpretation of single estimations of serum 170H‐progesterone are