Introduction. Regarding to the absence of doccumented studies concerning medial brachial coetaneous nerve conduction, the present study was conducted to evaluate this parameter as a diagnostic method for injuries to medial cord and lower trunk of brachial plexus. Methods. The sensory nerve action potential of median, ulnar and medial antebrachial cutaneous nerves were recorded to show these roots (Cs-TV are intact. Then, the medial brachial cutaneous nerve was stimulated on the line that connects axilla to medial epicondyle (parallel with mid axillary line) at the junction site of coracobrachialis muscle to humerus recording was done 2 cm above the medial epicondyle (10 cm under stimulating site). Results. In all cases the wave was biphasic with primary negative phase. The latency was 2±0.3 ms-1 (range 1.4-2.6 ms-1) and the amplitude of SNAP was 30±10 mv (range 10-50 mV). The nerve conduction velocity was 61±4 ms-1 (range 53-69 ms-1). Discussion. With regard to the intensity and site of stimulation and recording area, this wave is not due to compound nerve action potential of median or ulnar nerve. This study may be useful in evaluation of T1 root and in differential diagnosis of medial cord and lower trunk lesions with ulnar and medial part of median nerve injuries.