Vibratory thresholds were continually measured with a variable-amplitude vibrometer during periods of controlled median nerve compression in 12 human volunteers. Tissue fluid pressure in the carpal canal was maintained at 50 mm Hg, a level which caused a complete loss of nerve function in all subjects by 45 minutes. In all subjects vibratory thresholds proved to be the earliest test indicating a decrease in nerve function. Semmes-Weinstein pressure testing and 256 cycles/sec vibratory sensibility correlated well with measurements of vibratory thresholds and with the electrodiagnostic testing. Static and moving two-point discrimination did not become abnormal until late in the clinical testing. The vibrometer has significant potential as a clinical and research instrument in nerve compression syndromes. This study supports the use of vibratory stimuli as a noninvasive diagnostic test; it is currently undergoing evaluation in a number of clinical studies.