Signs of hepatic regenerative activity were detected by radioactive thymidine incorporation and cariometry in hepatic parenchymal cells of mice infected with 30 cercariae of Schistosoma mansoni for 10 weeks and then submitted to partial (30%) hepatectomy. The same methods failed to detect regeneration in mice submitted to partial hepatectomy, to S. mansoni infection or to sham operation, as well as in normal control mice. The stimulus required for hepatic regeneration in the mouse apparently needs to be strong, as was the case when the effects of partial hepatectomy were added to those of S. mansoni-induced lesions. These data show that extensive schistosomal lesions do not impede hepatic cell regeneration by the mouse.