Previous ultrastructural studies of pleomorphic adenoma have presented conflicting results with regard to the role of myoepithelial cells in the histogenesis of this tumour. In the present study specimens of ten major salivary gland pleomorphic adenomas were examined ultrastructurally and a number of cell types identified. The material was subjected to quantification using the stereological method of point counting. The results showed a wide spectrum of differentiation within these tumours in which typical myoepithelial cells were rarely encountered even in situations where they are reported to occur in routine histological preparations. Cells with some myoepithelial features were more numerous but duct cells accounted for the majority of tumour cells. The ultrastructural findings correlated well with previously reported immunocytochemical data and further support certain ideas about salivary gland tumour histogenesis.