The technique of intraosseous infusion has attracted increasing interest in recent years, and has proven valuable for drug administration. This study was undertaken to determine whether it was also a potential route for fluid resuscitation. Thirteen- or eighteen-gauge tibial intraosseous needles were placed in eight "large" (mean weight, 14.4 kg) and eight "small" (mean weight, 5.8 kg) swine and the flow rate of blood and saline measured under gravity and 300 mm Hg. Flow was significantly greater using 13-gauge needles in the "large" swine, significantly greater for saline than for blood, and for pressure infusion versus gravity in all animals. A fluid bolus of 20 ml/kg could be given to all animals in less than 10 minutes using pressure infusion. These data suggest that intraosseous infusion is a reasonable initial step in fluid resuscitation of pediatric subjects until more conventional vascular access has been established.