Varying degrees of vascular occlusion can be found in the hemolytic-uremic syndrome (HUS). This is the rationale for Doppler sonographic investigations of renal blood flow in children with HUS. In 1989 a first report suggested a close relationship between normalization of the resistive index (RI) of renal blood flow with the restitution of urine flow in affected children. Later reports did not confirm these initial findings. The aim of this paper is to describe renal volume perfusion quantitatively in children with HUS. The renal arteries in 35 patients with HUS (1 month to 15 years) were investigated at the onset of HUS by color Doppler ultrasonography. Flow volume measurements were carried out in the 1st week and in the 2nd to 4th week after onset of the disease. These data were compared with measurements from a healthy pediatric population of 69 children. Statistically significant changes in renal perfusion occur in the flow volume of the kidneys. The flow volume dropped to 32% (34%) in the 1st week of the disease compared with the normal population and recovered in 2-4 weeks to 117% (65%) of the normal flow volume (left kidney in parentheses). The new technique of volumetric perfusion measurement overcomes some drawbacks of the traditional RI, which may have led to some confusion in the past.