In order to design procedures for adequate repair of vascular injury, we have conducted a study of arterial trauma caused by high velocity missiles. This report is concerned with the mechanism of arterial injury in ballistic wounds. The femoral arteries of anesthetized dogs were injured with missiles accurately calibrated at velocities of 1,000, 2,000, and 3,000 feet per second. The technique included angiograms of vessels at the moment of impact. High speed photographs demonstrated the sequential course of mechanical disruption with low and high velocity missiles. We have shown that the high velocity missile neatly shears the blood vessel wall at moment of impact. However, additional damage to the arterial wall, both gross and microscopic, is caused within 5μ to 10μ sec by the formation of the temporary cavity.