OBJECTIVE To investigate the effect of different transcutaneous electrical nerve stimulation (TENS) parameters on nerve conduction in the human superficial radial nerve and on peripheral mechanical pain threshold (MPT) and tactile threshold (TT), and to further the current knowledge of the neurophysiologic effects of TENS. METHODS Fifty healthy human subjects were randomly allocated in equal numbers to a control group or one of four TENS groups to receive electrical stimulation consisting of four combinations of TENS pulse durations (50microsec and 200microsec) and frequencies (4Hz and 110Hz). In the TENS groups, TENS was applied under double-blind conditions for 15 minutes over the superficial radial nerve in the dominant forearm. Over a 1-hour period, compound action potentials, MPT readings, and TT readings were recorded bilaterally. RESULTS Only one combination of TENS parameters (110Hz, 200microsec) effected consistent changes in all of the variables assessed, ie, TENS produced a significant increase in negative peak latency while simultaneously increasing both MPT and TT. CONCLUSIONS The findings from this study suggest that at least part of TENS-mediated hypoalgesia is a consequence of a direct peripheral effect of TENS, although a "central" effect may not be excluded.