The activity of lysosomal proteolytic enzymes (cathepsin A, B, C, D and E) in cytosol and in the liver homogenate and in the blood plasma of rats intoxicated with methanol and ethanol was measured 6, 12 and 24 h and 2, 5 and 7 days after the intoxication. The activity of all proteases was increased in the cytosol from 12h to 5 days of alcohols intoxication, whereas the activity of these enzymes was decreased in the liver homogenate during the same time. Ethanol caused a higher increase in cytosol proteases activity than methanol. The magnitude of the decrease in proteolytic activity in the liver homogenate depends on the amino acid active center of the enzyme and on the kind of alcohol. The greatest decrease was observed for sulfhydryl and hydroxyl proteases and a smaller one for carboxyl proteases. Moreover methanol caused a greater decrease than ethanol. It was shown that the lysosomal proteases activity in the plasma was increased from 12 h to 5 days after alcohols intoxication and ethanol caused only a little less changes than methanol. The increase in the liver lipid peroxidation products examined as tiobarbituric acid reactive substances was also observed at the same time. These results indicate that during methanol and ethanol intoxication the cellular and lysosomal membranes are impaired and proteases are translocated into the blood. However, changes in proteases activities and proteases distribution within the hepatocytes may lead to disturbances in the catabolism of cell proteins and to destruction of liver cells.