The viability and state of proliferation of cells in culture is conveniently assessed using MTT, which is metabolically reduced to stain functionally intact cells. The hypothesis was tested that this assay can also be used in the quantitation of effects of toxicants on hepatocytes in suspension. Hepatocytes isolated from BALB/c mice were incubated without or with menadione, rotenone, N-methylformamide or paracetamol. Cellular damage was measured by either MTT assay or release into the medium of lactate dehydrogenase (LDH). Results obtained with the two tests were compatible in the case of toxicity inflicted by menadione or N-methylformamide. Rotenone decreased cell viability as indicated by the MTT assay immediately after addition of the agent, whereas measurement of LDH release did not detect this rapid toxic effect. The MTT assay detected paracetamol-induced damage within the first hour of exposure, but this was not detected by the LDH assay until 3 hr had elapsed.