Eleven consecutive median nerves in patients with clinical carpal tunnel syndrome were examined prospectively with laser Doppler flowmetry. All procedures were done without a tourniquet with the patient under local or general anesthesia. Multiple measurements of median nerve blood flow were obtained during carpal tunnel release. Flow characteristics proximal to the transverse carpal ligament did not change after release of the ligament. Beneath the transverse carpal ligament, initial flow was random in 10 of 11 nerves. Within 1 minute after release of the transverse carpal ligament, flow became pulsatile and synchronized with the patient's pulse in nine nerves. Although preliminary, these data suggest that in carpal tunnel syndrome the segment of median nerve beneath the carpal ligament is relatively ischemic and this ischemia may be a factor in the development of symptomatic median nerve entrapment. The rapid return of a pulsatile signal within the nerve after release is positively correlated with relief or improvement of median nerve dysesthesias.