Bellini duct carcinomas have recently been identified as a new entity in the spectrum of renal cell carcinomas and 10 cases have now been reported. The present paper adds detailed clinical and morphological data on six new cases. In addition, immunohistological and electronmicroscopical results support the origin of these tumours from the renal collecting ducts, especially the papillary ducts (Bellini ducts). A set of immunohistological reactions, including reactions to cytokeratins 13 and 19, vimentin and UEA-1 was found to facilitate the differential diagnosis of Bellini duct carcinomas from other renal cell carcinomas and infiltrating urothelial carcinomas of renal pelvis.