Using a scanning microscope photometer we determined quantitatively the enzymecytochemical reaction product for naphthol-AS-D-chloroacetate esterase in neutrophilic granulocytes and their precursors in man. Evaluation of neutrophilic cells from three healthy donors resulted in a logarithm-normal distribution. After subdivision of these cells in their morphologically defined maturational stages no statistically bimodal distribution was shown within the single cell groups. Myelocytes showed twice the amount of the polymorphonuclear neutrophil absorption values. The highest promyelocyte obsorptions were double the values of the myelocyte absorptions. The standard deviation of the absorbance obtained with promyelocytes (which encompass cells already producing granules up to cells reaching their maximal granule content) was significantly higher than the standard deviation of the myelocytes. As already known, primary granules are only synthesized at the promyelocyte stage and - according to the present knowledge - their chloracylesterase and peroxidase activities are not lost during further maturation. Consequently, our results indicate that only enzyme-rich, late promyelocytes undergo mitosis transforming into myelocytes. Correspondingly, their absorption value was halved. Since the absorbance from myelocytes to polymorphonuclears is again halved, myelocytes divide only once. Metamyelocyte absorptions in part correspond to that of myelocytes. This indicates that no distinction can be made between myelocytes with mitotic capacity and "true" if only the size and the nuclear shape are considered metamyelocytes which are not longer capable of undergoing mitosis.