The pathology of schistosomiasis mansoni in rabbits was studied with special consideration to worm burden and duration of infection. Heavy and prolonged infections resulted in severe changes involving the intrahepatic portal vein branches, such as: polypoid endophlebitis, granulomatous endophlebitis and, later on, vascular occlusion and recanalization, vascular ectasia, fibrosis and hyalinization of the endothelial polyps. Living and dead adult worms, rather than the mature eggs, were the main pathogenetic factors. For some time the lesions tend to be limited to the portal vein branches, not extending to the periportal tissues, but, after 8 to 10 months, variable degree of portal, septal and intra-parenchymal fibrosis can be formed. However, both vascular and fibrotic changes in the liver had a focal distribution and therefore did not appear to cause portal hypertension and had no resemblance to the human pathology seen in cases of hepatosplenic schistosomiasis. Pathology of schistosomiasis in rabbits has peculiar aspects, which are worthwhile studying, since the model can be of interest for investigations, especially concerning the immunology and immunopathology of schistosomiasis mansoni.