Hypercholesterolemia attenuates endothelium-dependent vasorelaxation and augments the responses to vasoconstrictor agents. Both effects are largely due to a reduction in the release of endothelium-derived relaxing factor. Since endothelium-derived relaxing factor is now known to be nitric oxide derived from the metabolism of L-arginine, we hypothesized that the abnormal vascular response in hypercholesterolemia could be corrected by supplying the precursor to EDRF, L-arginine. In a series of studies, we have found that conduit and resistance vessels of hypercholesterolemic animals demonstrate endothelial dysfunction which is reversed after exposure to high concentrations of exogenous L-arginine. The experiments suggest that hypercholesterolemia induces a reversible dysfunction of arginine availability or metabolism.