To assess the accuracy of 2D phase-contrast magnetic resonance (2D PC MR) renal artery flow measurements, data obtained with this technique were compared with those acquired with the 133Xenon-washout procedure. In addition, the 2D PC MR flow data were related to functional renal information as derived from selective arterial and venous renin sampling. In 53 patients suspected of having renovascular hypertension, MR angiography of the renal arteries was performed, followed by a 3-step angiographic procedure: (1) selective venous and arterial renin sampling; (2) assessment of the renal blood flow by means of the 133Xenon washout technique, and (3) conventional renal angiography. After initial assessment, 71 kidneys were left for analysis. The overall prevalence of renovascular disease > or =50% stenosis was 18%. Mean renal blood flow as assessed with the 2D PC MR technique showed a significant correlation with the 133Xenon washout flow measurements, with a Pearson correlation coefficient of 0.69 (2-tailed; P<0.01). PC MR blood flow measurements correlated poorly with the presence and/or severity of renovascular disease on conventional angiography (r=0.1, P=0.36). Likewise, no statistically significant correlation with either renal venous renin levels or the renin ratio could be identified. Measurement of renal artery blood flow with the use of a 2D PC MR technique is technically feasible. However, the mean renal artery blood flow correlates poorly with either the presence of renovascular disease on angiography or with renin levels. Further improvement of this technique is necessary before it can be applied on a larger scale.