The ultrasonic flow detector was employed to assess distal flow whenever a question of limb viability existed following repair of 85 vascular injuries in Vietnam. In 21 limbs without palpable distal pulses after arterial repair or following disruption of the vascular repair, distal flow sounds were audible in 11, and each proved to have a viable extremity. Of ten limbs without audible distal flow, the six not revascularized proved to be nonviable and required amputation. The finding of good distal flow in casualties without palpable pulses following vascular repair assured limb viability and avoided many unnecessary reoperations at a less than ideal time. The presence of adequate distal flow allowed simple ligation of disrupted vascular repairs. With limb viability assured, needed revascularization could be deferred until infection had cleared, wounds had healed, and conditions were more ideal.