In early or mild carpal tunnel syndrome(CTS), conventional electrodiagnostic studies may show normal responses, In 50 hands from 50 control subjects and 16 hands from 10 CTS patients, mean values for latencies and amplitudes of the median and ulnar nerve were obtained, and then difference(median-ulnar) and ratio(median/ulnar) were calculated.

The difference of distal latencies(median-ulnar) and distal latency ratio(median/ulnar) to ulnar in control and patients group were statistically significant. The amplitude ratios of median ot ulnar sensory action potentials in control and patients group were 1.23 and 0.80, respectively, and the difference between two groups were statistically significant.

Using discriminant analysis, it is suggested that the sensitive diagnostic methods of CTS are the ratio of median sensory latencies stimulated at palm and wrist. the latency of median sensory nerve stimulated at wrist, the latency of median motor nerve stimulated at wrist and the difference between the distal motor latencies of median and ulnar nerve, in order of sensitivity.