Large disparity in experimental conditions concerning the use of isolated perfused liver led us to investigate the effects of two free-fatty acids on amino acid metabolism in this model. Oleate uptake was 210 +/- 46 nmol/min.g and octanoate uptake 550 +/- 60 nmol/min.g. Fatty acid utilization led to an increase in ketogenesis, enhanced by octanoate in accordance with its known availability for beta-oxidation. In our experiments neither oleate nor octanoate modified hepatic amino acid exchange and metabolism as assessed by the measurements of amino acids fluxes and glucose and urea production.