The diagnosis of brachial plexus nerve compression is controversial due to the subjective nature of patient symptoms and the lack of objective, quantifiable tests. It has been hypothesized that quantitative sensory evaluation of sensory threshold is the most sensitive method of evaluating nerve compression, particularly in the early stages. This study evaluated the sensitivity and specificity of vibration thresholds for detection of brachial plexus nerve compression. A multiple-frequency vibrometer was used to evaluate 40 control subjects and 35 patients with brachial plexus nerve compression. Calculated sensitivity values were modest (0.49 at 63, 250, and 500 cps) with high specificity values (0.98 at 8 cps) for individual frequencies using a fifth percentile criterion. The low sensitivity values indicate that this instrument is not adequate as a screening device.