Sonography of the subclavian veins is a new noninvasive, simple technique to evaluate the subclavian veins. The physiologic changes of the subclavian veins consistently respond in a predictable manner to simple respiratory maneuvers. The subclavian veins of 11 normal patients (22 veins) whose ages ranged from 18 to 60 years were studied. The most significant change in subclavian vein anteroposterior diameter during respiratory maneuvers (Valsalva/expiration/inspiration) occurred with inspiration (P less than .005), particularly during a sniff, with a mean decrease in diameter of 61%. This baseline evaluation establishes normal sonographic criteria of the subclavian veins. We suggest that real-time ultrasound using a high resolution transducer offers a rapid, reproducible, objective method of evaluating the subclavian vein directly.