This paper sought to determine biological properties of oncocytoma cells, both in vivo and in vitro, which may serve as useful diagnostic indicators. Cell lines were grown in short-term culture from two renal oncocytomas following enzymatic dissocation, characterised by immunohistochemistry and electron microscopy, and further studied for abnormal p53 or retinoblastoma genes. Cells in culture were shown to maintain the morphological attributes of the primary lesion, including the overproduction of mitochondria. Despite the absence of vimentin staining in the primary tumour, cells in culture were shown to express this intermediate filament. Immunohistochemistry for P53 protein demonstrated an overexpression in one of the tumours, suggesting that mutation had occurred. Restriction fragment length polymorphisms of the retinoblastoma and the p53 genes were not demonstrated. Mutation of the p53 gene does occur in oncocytomas. The maintenance of the phenotype of oncocytoma cells in culture suggests that in vitro studies may be useful in the identification of unique properties of the tumour.