A randomized placebo-controlled trial to assess the effects of L-arginine on functional status was performed in patients with peripheral arterial disease. Blood flow was assessed by Doppler and plethysmography and measures of nitric oxide synthesis (plasma and urinary nitrogen oxides) were performed. The effect of L-arginine on treadmill walking distance was determined. The potential for L-arginine induced angiogenesis was assessed using magnetic resonance angiography.