Either the color and the power Doppler have given important information on renal haemodynamics, but these methods are limited. The power directional Doppler (pdD) surpasses such limits; again, administration of Levovist increases the intensity of vascular signal. The aim of this study is the evaluation, in subjects with a solitary kidney, but without evident nephropathies, the morphology, the cortical vascularization and the functional status of the kidney. We studied 21 patients divided into three groups. Group A: subjects with normal renal function; group B: patients with caliceal and pielic dilation; group C: patient with chronic renal failure (CRF). In all subjects, a pdD was effected. Only in three patients it was necessary to administer Levovist, in order to emphasize the parenchymal vascularization. The A group subjects, on echographic B-mode examination, presented a normal morphology and volume of the kidney; on pdD exam, a regular intense and homogeneous parenchymal vascularization, with resistance index (RI) = 0.53 divided by 0.66. In B group, pdD showed an irregular vascularization, with RI > 0.7; also the glomerular filtration rate (GFR) was reduced (70 ml/min). In C group, at the pdD it was relevant a reduced and irregular vascularization in whole renal tissue. If possible, the echographic B-mode examination must be completed with the pdD, with or without Levovist, in order to identify unknown renal pathologies, moreover in subjects with a single kidney.