Basic differences and similarities of flow and static cytophotometric instruments are viewed with regard to technical peculiarities and applicability in the fields of biology and tumor pathology. In flow systems, precision of the information concerning quantities of constituents is high, whereas precision of information concerning morphologic parameters is low. In static systems, morphologic identification by a trained operator can be used advantageously to classify any given cell interactively, thus replacing a large number of flow parameters. This is why the vast majority of automated static machines used in pathology are still more or less semiautomatic or interactive. Carefully performed specimen-adapted cell preparation procedures in which each step is strictly supervised, highly standardized staining methods, and internal controls are prerequisites in order to obtain reliable cytochemical results. In a number of human tumors with well-controlled cytopathologic and/or histopathologic and clinical data, quantitative cytochemical analysis has been demonstrated to provide diagnostic and prognostic information complementary to that obtained by conventional clinical and morphologic methods.