When hepatocytes prepared from 24-h-fasted rats were washed, suspended and incubated in Krebs-Henseleit bicarbonate-buffered saline, the endogenous rates of O2 consumption and heat production were 2.13 +/- 0.13 mumol/min per g wet wt. and 1.00 +/- 0.05 J/min per g wet wt. respectively. The inclusion of 2.5% (w/v) defatted and dialysed bovine serum albumin in either the cell suspension (washing) buffer or the cell incubation buffer produced a 20-25% increase in O2 consumption and heat production: these rates were increased by an additional 20-25% when the albumin (2.5%) was present in both the cell suspension and the cell incubation buffers. There was an inverse relationship between the increases in O2 consumption and heat production and the leakage of lactate dehydrogenase from the isolated hepatocytes: the inclusion of purified bovine serum albumin decreased lactate dehydrogenase leakage from 40% to 15% of total enzyme content. The calorimetric-respirometric ratios for hepatocytes incubated both in the absence (-461 +/- 19 kJ/mol O2) and presence (-477 +/- 8 kJ/mol O2) of the purified protein are very similar to the theoretical, thermochemically derived oxycaloric equivalents.