In their recent report, Olin and colleagues ([1]) state that a renal artery end diastolic velocity of 150 cm/sec or greater is an important criterion for diagnosing critical renal artery stenosis. This appears to be correct; however, for an end diastolic velocity of 150 cm/sec to have a high clinical utility, values less than 150 cm/sec should be helpful in identifying arteries that lack critical stenosis. Figure 3 of Olin and colleagues' report shows that this is clearly not the case ([1]). Several investigators have shown that end diastolic velocity correlates inversely with serum creatinine levels ([2]). Therefore, with significant renal parenchymal disease, end diastolic velocity may be reduced, even in the presence of critical renal artery stenosis. It is important to identify these patients, given that a low end diastolic velocity does not preclude beneficial blood pressure or renal function response in patients having revascularization ([2]). We recently reported that renal artery stenosis commonly occurs in older patients who are beginning renal replacement therapy ([3]). In these patients, end diastolic velocity was successfully measured in 80 consecutive nonoccluded arteries. The results are shown in Table 1. Although arteries with critical renal artery stenosis had a significantly higher end diastolic velocity than arteries without critical stenosis, overall end diastolic velocity was low. Peak systolic velocity was greater than 200 cm/sec in all arteries with critical stenosis and less than 200 cm/sec in all arteries without critical stenosis. In summary, an end diastolic volume of greater than 150 cm/sec may not be a highly useful criterion to identify critical renal artery stenosis because critical stenoses frequently occur with an end diastolic velocity of less than 150 cm/sec.