Ultrasonography is currently the method of choice to examine the pediatric patient because it is widely available, noninvasive and inexpensive. Particularly, Doppler US is the method of choice to study renal artery stenoses, which are among the most frequent causes of arterial hypertension in children, in both renal allografts and native kidneys. This study was aimed at investigating the value of the indirect signs of stenosis observed during the assessment of intrarenal vessels--i.e., changes in the waveform, resistive index and acceleration index. We examined 63 renal allograft recipients and a 12-year-old boy with a native kidney and arterial hypertension. In all cases the Doppler curves of the intrarenal vessels were studied both qualitatively and quantitatively. In this paper we report on 5 cases (4 allografts and 1 native kidney) with major waveform changes in the downstream renal circulation. Our findings confirmed the resistive index and the acceleration index measured with Doppler US in the intrarenal vessels to be major diagnostic tools in renal artery stenoses in the pediatric patient when the renal arteries are difficult to assess. However, the technique exhibits some limitations and allows an unquestionable diagnosis only in severe stenoses.