The blood flow through the hemofilter device is the key point for ultrafiltrate production during continuous arteriovenous hemofiltration. It mainly depends on arteriovenous pressure gradient and vascular access, which is the major problem for arteriovenous hemofiltration in infants and small children. In infants, we inserted short 18-20 gauge catheters into the radial or brachial artery and the internal jugular vein and achieved mean blood flow and ultrafiltration rates of 6.5 +/- 2.2 and 1.3 +/- 0.3 ml/min, respectively. In small children, we placed 4 or 5 French catheters into the femoral vessels, and achieved mean blood flow and ultrafiltration rates ranging from 18.5 to 63.6 and 1.9 to 6.9 ml/min, respectively. The only catheter-related complication was a femoral artery thrombosis, which needed surgical revision. These results show that vascular access for arteriovenous hemofiltration in infants and small children provides sufficient blood flow through the device for ultrafiltrate production.