In the present study we have localized neutral phosphatase, acid phosphatase, alkaline phosphatase and 5' nucleotidase in the sinusoidal cells of rat liver using enzyme cytochemistry at light and electron microscopical level. Neutral phosphatase was present in the endoplasmic reticulum and nuclear envelope of parenchymal cells and of sinusoidal endothelial, Kupffer and fat-storing cells. The intensity of the neutral phosphatase reaction was stronger in sinusoidal than in parenchymal cells. Sinusoidal cells were devoid of cytochemically demonstrable alkaline phosphatase. Abundant acid phosphatase was present in the many lysosomes of endothelial and Kupffer cells. Substantially less acid phosphatase-positive lysosomes were found in fat-storing cells. 5' nucleotidase was present on the cell membrane of fat-storing cells, on 90% of all Kupffer cells and on the microvilli of parenchymal cells. We have further shown that combined staining for 5' nucleotidase and for endogenous peroxidase, offers a histochemical tool to discriminate between the three main sinusoidal cell types in normal rat liver.