Hepatocytes from rats treated with phenobarbitone were exposed to 10 mM paracetamol for 1 hr and then incubated in buffered Ringer solution. Enzyme leakage and trypan blue entry became severe in the paracetamol treated cells some 2 hr after the end of exposure. These signs of cell injury could be blocked by 4 mM CaEDTA added during or after paracetamol exposure. CaEDTA did not alter covalent binding of [14C]paracetamol. Ca2+ free media did not prevent paracetamol injury. Lipid peroxidation was observed in cells but could be blocked without protecting the cells. Protein synthesis was depressed early on in cells previously exposed to paracetamol, CaEDTA did not protect against this inhibition. These observations suggest that an early cytoplasmic lesion develops into a later lethal lesion at the cell surface.