The serum α-fetoprotein level was measured by radioimmunoassay in 200 patients when admitted to hospital, 63 with idiopathic hemochromatosis and 137 with liver cirrhosis. In addition, repeated controls were performed in 19 subjects of each group for a mean period of 11 months (range 3–18 months). Elevated α-fetoprotein levels were observed initially or during the study period in 15 patients, a malignant liver tumor being demonstrated in 12 of them. In 4 of these patients, the abnormal α-fetoprotein concentration was the clue to the diagnosis of an unsuspected malignant hepatoma, but in none of these cases could the tumor be resected. The present results indicate that screening the serum α-fetoprotein level may contribute to the detection of malignant hepatoma in high-risk clinical groups, but the practical interest of such screenings may keep limited until more efficient therapeutic methods are deve