CYCS and neoplasm: The data presented in this study provide evidence that the apoptosome (i.e. the caspase-activating complex that is formed upon release of cytchrome c) is structurally and functionally intact in cells from RCC cell lines and primary RCC, at least when investigated by the addition of exogenous cytochrome c. Although, with the method used, a population of totally pure primary tumour cells could not be obtained, eight out of 20 samples contained over 90% of tumour cells, and this appears as a purity that is likely high enough to obtain results relevant to the tumour cell population.