In the published literature relating to flow-mediated dilatation (FMD), there are substantial differences between centres in terms of normal FMD amongst healthy subjects. This present study attempts to identify the effect of differing methodologies on FMD. High frequency ultrasound was used to measure blood flow and percentage brachial and radial artery dilatation after reactive hyperaemia induced by forearm or upper arm cuff occlusion in 24 healthy subjects, less than 40 years, without known cardiovascular risk factors. FMD of the brachial artery was significantly higher after upper arm occlusion, compared with forearm occlusion, 6.4 (3.3) and 3.9 (2.6)% (P<0.05), respectively. FMD of the radial artery was significantly higher after forearm occlusion, compared with upper arm occlusion, 10.0 (4.6) and 7.9 (3.5)% (P<0.05), respectively. The percentage blood flow increase in the brachial and radial arteries after forearm and upper arm occlusion were similar. After forearm and upper arm occlusion, the radial artery percentage dilatation was greater than the brachial artery. In conclusion dilatation of the brachial artery, after reactive hyperaemia induced by upper arm occlusion, was significantly more pronounced compared with dilatation of the brachial artery after forearm occlusion, despite a similar percentage blood flow increase. The local ischaemia of the brachial artery with a proximal occlusion may explain why the brachial artery dilated more after upper arm occlusion compared with after forearm occlusion. The study has also shown that FMD of the radial artery could be assessed by B-mode ultrasound technique. FMD was greater using the radial artery compared with the brachial artery, suggesting that the radial artery may be a useful way to assess FMD in future clinical studies.