Cattles suffering from chronic enzootic haematuria frequently develop urinary bladder tumours of both epithelial and mesenchymal origin mainly haemangioma and its malignant counterpart. The role of the bovine papillomavirus type-2 (BPV-2) and of its major transforming oncoprotein in naturally occurring urothelial carcinogenesis has been recently clarified. E5 interacts in vivo as in vitro with the beta receptor for the platelet-derived growth factor (PDGF). However, studies regarding tumours of mesenchymal origin such as those arising from blood vessels are lacking. We show that the BPV-2 is present in 100% of the vascular tumours of the urinary bladder examined. Twenty-six out of twenty-seven tumour samples (96%) expressed E5 while 20 out of 27 (74%) tumour samples expressed E7. The two viral oncoproteins were not expressed in normal endothelial cells. Additionally, they co-localize in neoplastic endothelial cells as demonstrated by confocal immunofluorescence. PDGFbeta receptor was also shown to be expressed and co-localizes with E5 in neoplastic blood vessels. Our results demonstrate, for the first time, that the BPV-2 is present in high percentage in tumours of mesenchymal origin arising in its natural host. Furthermore, the expression of the two viral oncoproteins confirm that the virus may have a causative role in the neoplastic process.