Large volumes of an anesthetic solution used during regional axillary anesthesia may produce elevated pressures within the axillary sheath that lead to arterial compression and diminished blood flow. We measured axillary sheath pressure as a function of injected volume in 20 patients scheduled for hand surgery. Bupivacaine without epinephrine was injected into the axillary sheath in 10-ml increments until a cumulative volume of 50 ml was attained. Elastance (ΔP/ΔV), where ΔP equals change in pressure (mm Hg) and ΔV equals change in volume (ml), was 0.8 ± 0.1 (± SEM) mm Hg/ml in successful block and 0.09 ± 0.1 mm Hg/ml in unsuccessful blocks. Axillary sheath pressure did not exceed mean arterial pressure for periods longer than 60 s. We conclude that vascular insufficiency resulting from arterial compression following axillary block anesthesia is unlikely.