In view of accumulating evidence of vascular pathology in Alzheimer's disease (AD), we tested the hypothesis that AD patients have impaired endothelial function. This was assessed using the technique of strain-gauge venous occlusion plethysmography, which measures forearm blood flow (FBF). Intra-arterial (brachial) infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) was used to assess local endothelial dependent and independent responses, respectively. There was no difference in the basal FBF of patients and controls. ACh and SNP caused dose-related increases in FBF from baseline, but no difference was recorded between the AD and control group. This study provides no evidence of endothelial dysfunction in the systemic circulation of patients with AD.