1. Endothelial dysfunction, due to reductions in nitric oxide (NO) action, is an early feature of macrovascular disease. 2. Non-invasive measurement of endothelial function may be assessed by postischaemic dilation of forearm vessels, using plethysmography, or flow-mediated dilatation of the brachial artery, using ultrasound. 3. Brachial flow-mediated dilatation reflects NO release and/or action more than forearm hyperaemia. 4. These techniques have been used as surrogate measures of coronary endothelial function. 5. Methodological, physiological and clinical aspects of the techniques are discussed.