A combination technique of a telemetric system and a Walter-type analyzer have been used in the rat to allow on-line display of the sleep-waking cycle of a freely-moving animal on three consecutive days. 2. The characteristics of slow-wave sleep can be analyzed completely by this technique. 3. Telemetric recording of the integrated slow wave is a good method that allows faster and accurate scoring of slow waves to measure the length of sleep in freely-moving animals.