Seventeen children with acute renal failure due to the hemolytic-uremic syndrome were examined with duplex Doppler ultrasound. Serial measurements of intrarenal arterial pulsatility were obtained by means of the Pourcelot index. These were compared with daily urine volume, both during the phase of renal failure (during which most of the children were undergoing peritoneal dialysis) and during recovery of renal function. During oliguria or anuria there was either no intrarenal arterial flow (ie, absent Doppler shifts), or absent, reversed, or markedly reduced diastolic flow. Within 24-48 hours after diastolic Doppler shifts returned to normal, diuresis occurred. The Doppler examination enabled prediction of recovery and allowed dialysis treatment to be abbreviated or, in some cases, canceled.