The cerebral hemodynamics in healthy and ill children are studied systematically for the first time using transcranial Doppler sonography (TCD). The blood flow velocities in the various basal cerebral arteries are determined from the Doppler shifts. Unlike other Doppler techniques, TCD can be used in patients of all ages. It produces reliable results, even without visualization of the region of the brain being examined. The results are comparable with those of other methods.