The pacemaker activity of longitudinal muscle, as reflected by in vitro rhythmic contractions of the adult male rat's duodenum, has been examined in terms of intercontraction intervals that were collected using a microprocessor-based system. For each duodenal segment studied, 512 consecutive intercontraction intervals were classified into 25 msec. increments from 25 msec to 5 seconds. The resultant frequency histogram was characterized by its first four sample cumulants. Duodenal segments exposed to different temperatures were analyzed to see if changes in the distributional characteristics of the intercontraction intervals could be observed in response to the controllable environmental condition of a water bath. The mean intercontraction interval decreased linearly with an increase in temperature. While the intercontraction interval histograms generally were positively skewed and leptokurtic, no significant changes in these characteristics could be detected at different temperatures. This approach suggests the usefulness of duodenal segments in physiological, pharmacological and toxicological studies.