Developmental disturbances and encephalopathy have been observed in children with chronic renal failure (CRF). The aim of this study was to investigate the efficiency of the cerebral circulation in uremic children. The study group consisted of 10 children with CRF on conservative treatment, 8 children on continuous ambulatory peritoneal dialysis (CAPD), and 8 children on maintenance hemodialysis (HD). Examination was performed using a TC2-64B, EME Doppler flowmeter machine and capnograph Datex, Normocap. Blood flow velocity in both middle cerebral arteries (MCA), at rest and after spontaneous hyperventilation for 30 s, was analyzed. The vascular reactivity coefficient was calculated as the percentage ratio of decline of blood flow velocity in MCA to PCO2 decrease. Baseline mean blood flow velocities of MCA in euvolemic children under conservative treatment and on CAPD were significantly higher than those in children on HD and healthy control children. The highest value of the vascular reactivity coefficient was significantly higher in the group of children with CRF on conservative and CAPD treatment, than in children on HD and healthy controls. We suggest that hyperreactivity of the cerebral circulation could be the result of impaired autoregulation of blood flow. Evaluation of cerebrovascular reactivity in uremic children requires further examination.