Endothelial function is routinely assessed by non-invasive techniques but is expensive and requires skilled technicians precluding its routine use as a clinical tool to predict cardiovascular disease risk. Commonly assessed in the brachial artery, due to access and calibre similarities to the coronary circulation, dysfunction is defined as an inability of the artery to dilate in response to reactive hyperaemia. Recently changes in carotid-radial pulsewave velocity have been suggested as an alternative method to measure endothelial function. Moreover, changes in arterial distension following reactive hyperaemia should provide similar predictive utility, but has not been evaluated. Eleven participant’s (female=4) attended the laboratory on up to 4 occasions and underwent repeated vascular function protocols. Ischaemia-reperfusion injury was induced on each occasion to reduce endothelial function thus providing a range of flow-mediated dilation (FMD) values within each participant. Trials were also preceded by one of four experimental conditions to further provide a range of FMD values. Participants ingested either: 1) water ad libitum, 2) an antioxidant cocktail at 2 and 1.5 hours, 3) 1200mg Ibuprofen 1 hour prior; or 4) a combination of 2 and 3 in a blinded fashion. FMD was determined using an Aloka Alpha6 Doppler ultrasound system. Diameters were acquired at 2MHz before and after a 5-minute forearm occlusion period. The spatial resolution of diameter measurements was 0.05mm acquired using echotracking. The time delay between the R-wave of the ECG and the foot of the diameter waveform were used to calculate pulse transit time (PTT). Maximal relative change in PTT was determined as (PTTmax-PTTmin)/PTTmin x 100%. Brachial artery distension was determined on a beat-by-beat basis throughout the reactive hyperaemia period and maximal relative change was determined as (distension max-distension min)/distension min x 100%. Relationships between the three measurement modalities were determined by correlation analysis using Pearson product-moment correlation coefficient. Significance was assumed if p≤0.05. No relationship was observed between pulsewave velocity and FMD (r=-0.113, p=0.352) or absolute FMD (r=-0.003, p=0.98). Furthermore, no relationship existed between the change in brachial artery distension and FMD or absolute FMD (r=0.03, p=0.80; r=-0.006, p=0.96 respectively). The results of this study suggest that non-invasive measures of vessel stiffness changes induced by reactive hyperaemia do not represent an adequate assessment tool for measures of endothelial function within the brachial artery. Flow-mediated dilation remains the ‘gold-standard’ for non-invasive measurement for assessment of endothelial function.