beta-Glucuronidase activity is elevated in the urine of patients with bilharziasis hematobium. In the present study the enzyme level was estimated in whole urinary bladder tissue homogenates of mice experimentally infected with Schistosoma mansoni. In the infected mice the enzyme activity is significantly higher than in the controls. The effect of the schistosomicidal drug hycanthone was also evaluated. Treatment with the drug did not affect the level of the enzyme activity in the infected mice; it induced an increase in the enzyme activity of the controls.