Serum-25-hydroxy-vitamin-D (25 OHD) concentration has been measured in 106 patients with untreated parenchymal and cholestatic liver disease. Low mean values were found in groups of patients with alcoholic hepatitis and cirrhosis, non-cirrhotic active chronic hepatitis, lupoid and cryptogenic cirrhosis, symptomatic primary biliary cirrhosis, and acute and chronic biliary disease. In a group of patients with presymptomatic biliary cirrhosis the mean value was not significantly different from normal. It is concluded that in the presence of significant parenchymal or cholestatic liver disease serum-25-OHD concentrations are usually low. The mechanisms for the reduction remain to be clarified, but low serum-25-OHD values may play a contributory role in the aetiology of osteomalacia in chronic liver disease.