Like all steroid hormones, androgens are extensively metabolized in the liver. The metabolism results in inactive steroids which are thereafter eliminated mainly in the urine. Three types of reaction are essential: oxidation of the 17β-hydroxy group, reduction of the double bond and of the 3-keto group, and conjugation with glucuronic or sulphuric acid. Thus the main urinary metabolites of androgens are 17-ketosteroids with a reduced A ring. The existence of 5α-, 3α- and 3β-reductases has been demonstrated in the liver.