Nocturnal clenching and grinding can be recorded with a portable electromyograph unit and a standard cassette tape recorder, which registers the clenching episodes on a cassette tape. The information can then be coded by a new instrument, called a Pulse Identifier, that subsequently transfers the data to a polygraph chart recorder. This study evaluated the reliability and validity of the Pulse Identifier when interfaced with other instruments that measure nocturnal clenching/grinding. A known number of clenching incidents over a baseline period of time were evaluated by three lind scores. The results demonstrated an interscorer reliability coefficient of 0.99 and a validity coefficient of 0.99.