The purpose of this study was to determine the effect of conventional low-intensity transcutaneous electrical nerve stimulation (TENS) waveform and frequency characteristics on experimentally induced acute pain. Each of 28 male subjects received six forms of TENS and one control treatment during a single testing session. Treatments used one of two waveforms (monophasic or biphasic) and one of three frequencies (30, 60, or 85 Hz) administered to the forearm. Treatment effects were ascertained from alterations in pain-threshold and pain-tolerance responses induced by noxious electrical stimulation of the ipsilateral fifth digit. The TENS waveform and frequency had a negligible effect on pain threshold. The results indicated that waveform did not influence pain tolerance significantly. Pain tolerance, however, increased significantly at the frequency of 60 Hz but decreased significantly at both 30 and 85 Hz (p less than .05). We concluded that TENS frequency is an important factor in altering the subjects' perception of experimentally induced pain.