We administered a step I diet to 50 hypercholesterolemic patients with coronary artery disease during 12 weeks. Compared with baseline, the step I diet significantly changed lipoprotein levels, significantly improved the percent flow-mediated dilation response to hyperemia by 32 +/- 7% (p <0.001), increased plasma levels of nitrate by 45 +/- 12% (p = 0.013), and lowered plasma levels of malondialdehyde by 7 +/- 4% (p = 0.011). However, the step I diet did not significantly change serologic markers of inflammation, plaque stability, and thrombosis. Step I diet therapy improved endothelium-dependent vasodilation with an increase in plasma nitrogen oxide and a decrease in oxidant stress in hypercholesterolemic patients with coronary artery disease.