The effect of endotoxin administration on free fatty acid (FFA) utilization by skeletal muscle was investigated. Albumin bound [1-14C]palmitate was continuously infused into anesthetized dogs. Blood samples from the carotid artery and profunda femoris veins were obtained and blood flow through the thigh muscles was determined. After endotoxin, skeletal muscle blood flow decreased by 29%, reflecting the average decrease in cardiac output. Arterial FFA concentration in endotoxin-treated animals was significantly reduced relative to saline-treated animals. Whole-animal FFA turnover decreased up to 37% after endotoxin. FFA uptake was linearly correlated with arterial FFA concentration both preceding and following endotoxin and the slopes of the regression lines were identical. FFA uptake by skeletal muscle was significantly reduced during the early postendotoxin time period. Skeletal muscle FFA oxidation after endotoxin also tended to decrease. It is concluded that the changes in skeletal muscle FFA metabolism are most likely due to decreased arterial FFA levels after endotoxin rather than a direct effect of endotoxin on skeletal muscle.