Spontaneous continuous arteriovenous hemofiltration (CAVH) may fail to control azotemia in small patients with renal failure due to poor blood flow. To produce adequate ultrafiltrate a continuous negative pressure was added to the ultrafiltrate line. Two hemofilter systems of different membrane and surface area were used. Suction support approximately doubled ultrafiltration rate in both hemofilters. No side effects such as severe hypotonia or early hemofilter clotting occurred. Added suction can serve as a useful support of spontaneous CAVH in children with renal failure and too poor a blood flow to control azotemia.