The main complication of Schistosomiasis is the development of liver fibrosis as a result of periovular granuloma in portal tract. This study was undertaken to evaluate the role of the worms in the liver, using the unisexual murine schistosomiasis model. Hepatic fibrosis and histopathological lesions were sequentially followed for 65 weeks in mice experimentally infected with male Schistosoma mansoni. Morphological study revealed that, from the 25th week post-infection, a diffuse fibrosis affected the main branches of the portal vascular system following the host inflammatory reaction, associated with the proliferation of myofibroblasts in situ. Quantitative methods confirmed that an increase of fibrotic deposit occurred during chronic unisexual infection from 25 to 50 weeks post-infection, as compared to controls (35.06 +/- 3.55% versus 27.41 +/- 2.56%) suggesting that antigenic substances secreted by adult schistosomes, in the absence of any eggs, might initiate periportal and perisinusoidal fibrous reaction. The cytokine production and the evolution of inflammation towards fibrosis involves stellate cells and myofibroblasts stimulation. This fibrotic process consequently traduces a reparative phenomenon of the liver.