The activities of the two kinetic components (high and low affinity) of the microsomal 0-deethylation of 7-ethoxycoumarin have been measured in liver from patients with alcoholic cirrhosis and in normals. The activity (expressed as pmol 7-OH coumarin formed/mg microsomal protein/min) of both components of the enzyme was significantly lower in alcoholic cirrhosis (high affinity = 3.27 +/- 1.18, low affinity 60.9 +/- 11.6) than in normals (high affinity 9.43 +/- 2.37, low affinity 111.3 +/- 9.2). These results are further evidence that there is a broad impairment of hepatic microsomal mono-oxygenase activity in alcoholic cirrhosis.