Differential response of freshly isolated rat hepatocytes to paracetamol (acetaminophen, AAP), carbon tetrachloride (CCl4) and D-galactosamine (GalN) was examined. The viability of the cells in suspension culture was not altered for 4 hr when incubated in Hank's balanced salt solution (HBSS) supplemented with 4.2 mM NaHCO3, 10 mM HEPES buffer and 0.5% bovine serum albumin. AAP induced time and dose dependent depletion of GSH as an early manifestation of AAP toxicity. Hepatocytes exposed to AAP exhibited lower lactate dehydrogenase (LDH) activity released into the medium than in controls. This was due to the interaction of a reactive metabolite of AAP, i. e. N-acetyl p-benzoquinoneimine (NAPQI) with cell proteins. Hepatocytes isolated from rats pretreated with 3-methylcholanthrene expressed higher sensitivity to AAP toxicity at least by a factor of 5. Furthermore, AAP-induced toxicity was not found to be related to any lipoperoxidative stress. CCl4 on the other hand elicited a highly lipoperoxidative response in hepatocytes and consequent leakage of cellular enzymes with lengths of incubation. Again the sensitivity of the response to CCl4 was enhanced remarkably in hepatocytes isolated from phenobarbital- pretreated rats; LDH leakage increased by 3-fold and thio-barbituric acid reactive substances by 25-fold. Unlike the two toxicants, galactosamine depleted UDP-glucuronic acid in a concentration and time-related manners. The differential biochemical response of hepatocytes to three hepatotoxicants investigated may prove useful as rapid in vitro screen for selection of compounds of hepatoprotective potentials.