The change in the expression of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities in neoplastic colon and lung prompted us to study the possible effect of cancer on the expression of cholinesterases (ChEs) in kidney. Samples of papillary renal cell carcinoma (pRCC), conventional RCC (cRCC), chromophobe RCC (chRCC) and renal oncocytoma (RON), beside adjacent non-cancerous tissues, were analyzed. In pRCC both AChE and BuChE activities were statistically increased; in cRCC and chRCC only AChE activity increased and in RON neither AChE nor BuChE activities were affected. Abundant amphiphilic AChE dimers (G(2)(A)) and fewer monomers (G(1)(A)) were identified in healthy kidney as well as in all tumour classes. Incubation with PIPLC revealed glycosylphosphatidylinositol in AChE forms. BuChE is distributed between principal G(4)(H), fewer G(1)(H), and much fewer G(4)(A) and G(1)(A) species. RT-PCR showed similar amounts of AChE-H, AChE-T and BuChE mRNAs in healthy kidney. Their levels increased in pRCC but not in the other tumour types. The data support the idea that, as in lung tumours, in renal carcinomas expression of ChE mRNAs, biosynthesis of molecular components and level of enzyme activity change according to the specific kind of cell from which tumours arise.