ABSTRACT— The activity of the lysosomal enzyme, β-hexosaminidase, is increased in plasma of patients with various forms of liver disease as well as in plasma from rats with experimental cholestasis or cirrhosis. In this experimental study in the rat, the effect of porta-caval shunt, ammonia infusion and ethanol feeding on plasma β-hexosaminidase activity was studied. Porta-caval shunted animals had significantly increased plasma β-hexosaminidase activity compared to sham-operated animals. Ammonia infusion in porta-caval shunted rats resulted in a further increase of plasma enzyme activity. Ethanol feeding for different periods of time (1 day to 4 weeks) did not have any influence on plasma β-hexosaminidase activity.