A study on the beta-glucuronidase activity in liver and spleen homogenates of mice infected with an Egyptian strain of Schistosoma mansoni and of non infected control animals was carried out for a follow up period of four months. A decreased enzyme activity was observed in the spleen up to the 40th day after infection. From the 60th day on, the enzyme level in both liver and spleen was found above that in the control. The possible causes for such changes in enzyme activity are discussed.