Incubation of isolated rat hepatocytes under hypoxic conditions or in the presence of inhibitors of mitochondrial functions such as KCN or carbonylcyanide m-chlorophenylhydrazone (CCCP) causes an increase of intracellular Na+ content and cell swelling. Both these effects precede the appearance of irreversible damage as measured by trypan blue staining of non-vital hepatocytes. When the increase of cellular Na+ is prevented by substitution of NaCl in the incubation medium with equimolar amount of choline chloride both cell swelling and loss of viability are greatly reduced. Thus, we propose that osmotic stress induced by an uncontrolled accumulation of Na+ might be associated with the ultimate events precipitating irreversible membrane lesions in hepatocyte undergoing metabolic inhibition.