This study was aimed at establishing a baseline for the latency values of the biceps-brachii, triceps-brachii and brachioradialis tendon reflexes from the moment of elicitation by percussion of the tendon, to the appearance of the muscle action potential. The percussion hammer triggered the electronic sweep on the electromyograph oscilloscope, showing latency to the onset of the potential. Standard skin electrodes were used. Certain precautions were taken to avoid artifacts caused by skin movement. Thirty normal volunteer subjects, between the ages of 17 and 55 years, were examined. Biceps reflex latency values varied between 9 and 14 msec; with a mode of 11 msec and an average of 11 msec. Triceps latency values varied between 9 and 13 msec; with a mode of 11 msec and an average of 10 msec, and brachioradialis latency values varied between 13 and 20 msec, with a mode of 16 msec and an average of 16 msec.