Hepatic periovular schistosomal granulomas produced in mice with 50 cercariae per 10 weeks of infection were seen to involute following curative treatment of schistosomiasis. Residual scars remained, however, and the collagen tissue in them presented morphologic evidence of a slow, progressive degradation that lead to the almost complete disappearance of the lesions 4.5 months after chemotherapy. Ultrastructural changes indicative of collagen degradation were represented by focal lytic dissolution of collagen fibrils and/or by the transformation of such fibrils into a granular electron dense material, a picture different from that seen in more acute models of collagen resorption. In older, involuting granulomas, both type I and III collagens were found up to the end of the resorption process. The immunofluorescence staining for procollagen III and fibronectin correlated with collagen synthesis and the amount of both decreased as the granulomas involuted. Antibodies to CB-peptide (a2 CB3,5 from type I collagen) appeared as a good marker of acute collagen degradation only. Laminin and collagen type IV were absent from the granulomas. Periportal fibrosis produced in mice with 30 cercariae per 20 weeks of infection also presented progressive degradation of collagen 2 and 3 months following curative treatment of schistosomiasis. Present findings suggest that there is not an irreversible fibrotic stage in murine schistosomiasis, that chronic collagen resorption presents peculiar ultrastructural features, that the genetic collagen types are not differentially removed, and that periportal fibrosis in schistosomiasis undergo degradation in a way after specific treatment similar to periovular granulomas.