We have recently shown that elevated levels of free fatty acid (FFA) seen in insulin-resistant obese subjects are associated with endothelial dysfunction. L-carnitine, which is required for mitochondrial FFA transport/oxidation, has been reported to improve vascular function in subjects with diabetes and heart disease. Here, we tested the hypothesis that L-carnitine attenuates FFA-induced endothelial dysfunction. We studied leg blood flow (LBF) responses and leg vascular resistance (LVR) to graded intrafemoral artery infusions of the endothelium-dependent vasodilator, methacholine chloride (MCh). A group (n = 7) of normal lean subjects was studied under basal conditions (saline), after 2 h of FFA elevation (FFA), and then after 2 h of superimposing L-carnitine on FFA elevation. FFA elevation caused the maximal LBF increment in response to MCh to decrease from 0.388 +/- 0.08 to 0.212 +/- 0.071 L/min (P < 0.05). Similarly, FFA blunted the maximum decrease in LVR in response to MCh from -315 +/- 41 U to -105 +/- 46 U (P < 0.05). The superimposed L-carnitine restored the LBF increment in response to MCh to 0.488 +/- 0.088 L/min (P < 0.05 vs. FFA) and the maximum fall in LVR to -287 +/- 75 U (P < 0.05 vs. FFA), indicating that L-carnitine elevation may attenuate FFA-induced endothelial dysfunction. In conclusion, our data suggest that increasing L-carnitine levels may improve FFA-induced and obesity-associated endothelial dysfunction. This improved endothelial function may delay or prevent the development of excess cardiovascular disease.