Patients with chronic liver disease usually exhibit low plasma levels of testosterone with loss of libido and potency; this is also valid in male patients suffering from idiopathic hemochromatosis (IHC), in whom nowadays the diagnosis is made at an earlier age. Therefore, the effect of testosterone treatment was studied in 10 patients with IHC. After the application of 250 mg testosterone enanthate i.m., the plasma testosterone (from 2.4_+1.9 to 20.1_7.4ng/ml) and estradiol (from 17.4+6.3 to 38.5+14.2pg/ml) levels increased significantly. The rise of estradiol was in the range of controls and smaller than reported in other chronic liver diseases. In a long-term study, 250 mg testosterone enanthate was given 4weekly for 33-96 months to 5 patients with IHC. General well-being, libido, and potency recovered almost immediately. Over a treatment period of 27.3 patient years, symptoms of hyperestrogenism (gynecomastia) or (portal vein) thrombosis were not seen, both of which had been described in patients with alcoholic liver cirrhosis. There was no deterioration of liver function. The effect of testosterone treatment on the patients' well-being and plasma hormone concentrations remained unchanged over the whole period of testosterone treatment. Thus, in male patients with IHC and lowered plasma testosterone, treatment with testosterone enanthate may be instituted. Because of the positive effects on general well-being, liver regeneration capacity, and potency, testosterone should especially be administered to younger subjects suffering from IHC.