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The purpose of the study is a rigorous validation of different ultrasonic criteria of renal artery stenosis, and the presentation of the performances of duplex sonography in renal artery stenosis screening. Sixty seven patients have been investigated by ultrasonic techniques, and the results of duplex compared with intraarterial or intravenous digital subtraction angiography. Two kinds of ultrasonic investigations have been defined: complete explorations when the renal artery ostium is accessible, incomplete explorations in other cases. The main difficulty preventing the exploration from being complete is obesity: all patient with an overweight of more than 20% of their theoretical weight have an incomplete exploration of at least one of their renal arteries. Furthermore, duplex sonography was not able to demonstrate polar artery in any case. When the exploration is complete, maximum systolic frequency (F max) recorded on the renal artery course, and the systolic frequency ratio of renal and aortic recordings (RAR) are two valuable criteria of significant stenosis (> 50%): mean difference between normal and stenosed arteries for these two variables is statistically significant (p < 0.01). To obtain a good specificity, pathological threshold have been fixed at F max > 3,500 Hz and RRA > 2.5. When the exploration in incomplete, ascending time (asc. T) and resistance index (RI) of doppler recording obtained in the renal hilum are two valuable criteria for severe stenosis (> 80%), or occlusion: the mean between stenosed and non stenosed arteries is statistically different (p < 0.001 and p < 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)