Changes of fat metabolism in endotoxemic dogs were studied by means of intravenous fat tolerance test. Twelve dogs subjected to the present studies were divided into two groups; peritonitis was produced in one group (6 dogs) and 1.5 mg/kg of E. coli lipopolysaccharide was injected intravenously in another groups (6 dogs). After production of peritonitis, Limulus test was positive in all of the six dogs, however there were no significant changes in blood sugar levels, lactate/pyruvate ratio, and elimination rate of fat emulsion from the venous blood (K-value) after the induction of endotoxemia by peritonitis. On the other hand, a significant fall of the blood sugar levels and an increase of lactate/pyruvate ratio were found after the injection of endotoxin. A significant fall of K-value (from 0.0133 +/- 0.0056 to 0.0069 to 0.0024) was also observed in these six dogs. Results of the present studies suggest that the metabolism of fat emulsion is significantly affected by the intravenous injection of endotoxin, but not by the production of peritonitis if there is no disturbance of tissue perfusion.