The bilharzial granulomas and urothelial transformation are common findings in Schistosoma haematobium infested patients. We hypothesize that the distribution of extrinsic (fibronectin, FN) and intrinsic basement membrane (BM) proteins (laminin, LN) is altered during the evolution of these lesions. METHODS: To test this hypothesis, 70 cystectomy specimens, entailing variable associations of normal and dysplastic urothelium (all cases), and bilharzial granulomas were examined for FN and LN protein expression. RESULTS: Increased deposition for FN occurred with the evolution from cellular (loose fibrillary network, 20 cases) to fibrocellualr (dense fibrillary network, 30 cases) to fibrotic (tight conglomerates, 20 cases) granulomas. Alternatively, BM staining for LN was linear and continuous underlying normal and metaplastic urothelium. In dysplastic urothelium (20 cases), it showed breaks in continuity. CONCLUSIONS: Alterations of FN and LN occur during the development of the bilharzial granuloma and urothelial transformation.