Dilatation of the brachial artery occurs after flow is increased, and an attenuation in this response is seen in subjects with cardiovascular risk factors, and in those with established coronary artery disease. The mechanisms linking ischaemia, flow changes, and brachial artery dilatation are unclear, and it is not known how these are affected by arterial disease. For the present it might be more appropriate to refer to flow associated rather than flow mediated dilatation, to describe the phenomenon in the brachial artery. Despite these caveats, the non-invasive measurement of brachial artery following ischaemic dilatation represents a significant advance, and its suitability as a surrogate marker for coronary artery dysfunction appears promising. The technique has potential as a tool for screening those at high risk of vascular disease, and as a surrogate endpoint in intervention studies. Further research should clarify the mechanisms involved, and lead to greater insights into the nature of endothelial dysfunction and cardiovascular disease.