ABSTRACT— Experimental hepatic schistosomiasis was produced in CBA mice using a local strain of S. mansoni. A comparative study of the hepatic concentrations of cytochrome P-450 and microsomal protein in the control and infected animals was carried out. S. mansoni infection significantly (P<0.05) reduced the liver cytochrome P-450 and microsomal protein. This suggests impairment of drug metabolism in the liver of infected animals. The study calls attention to the possible clinical and pharmacokinetic implications of the late severe S. mansoni infection of the liver in man.