Carpal tunnel syndrome is a common entrapment neuropathy. Many Kinds of techniques have been developed for its identification. We collected 24 normal adults and 30 normal nerves to evaluate the radial and median sensory action potentials (SAP) recorded on the thumb, on wrist stimulation. The onset latency, peak latency, duration and amplitude of the radial and median SAP were analyzed. The interpeak latency of the two SAP was 0.13±0.12 msec. This interpeak latency may be very useful for early detection of carpal tunnel syndrome. An SAP of double peaks could be elicited on wrist stimulatin in carpal tunnel syndrome due to delaying of the median SAP.