Two studies are reported in which short pauses from the drinking behavior of four hooded rats (rat study) and four mice (mouse study) were analyzed. Both of these studies supported the hypothesis that the interlick interval (II) can be used as a unit (PC) for scaling short pauses in licking behavior during water drinking. The outcomes of these studies arc seen as suggesting that the factor responsible for the constancy of the II is also functioning during short pauses and is responsible for the tendency herein reported for pauses to be scaled by the PU, One may categorize biological rhythms, for convenience, into those which exhibit longer term cyclic behavior (such as seasonal or diurnal cycles) and phenomena with drastically shorter periods such as brain waves, heart rate, and water licking to name a few. At times we find certain biological activities, in both the short period and the long period categories, which exhibit a relatively constant periodic rate, suggesting that the animal and plant kingdoms have at their disposal biological "clocks," These clocks may rather accurately control certain processes which are facilitated by a stable rhythm of the appropriate periodic duration. Examples of obvious value to the animal world are the timing provided to insects in regulating their life cycle and the regulation of body metabolism in animals by diurnal cycles (Bunning, 1967). It is not so obvious, however, what function is served by the periodicity found in some of the behaviors exhibiting shorter periods. For instance, Stellar and Hill (1952) first established that rats, across a very wide range of water-deprivation levels. drink water at the relatively constant rate of 6-7 licks per sec. One might reasonably think that it would be desirable that a rat. when thirsty or in danger, be able to drink faster than it drinks when it is satiated. The fact is. however. that the satiated and the thirsty rat both drink at practically the same rate, Other studies (for instance, Keehn & Arnold, 1960) have replicated this remarkable stability of the lick rate for rats and also for cats (Schaeffer & Premack, 1961) and various other species (Boice, 1967), Control mechanismsunderlying such biological timing are not presently identified. Komisaruk (1970), in exploring the relation between rat theta activity, vibrissa t\\ itches, and heart rate, has suggested "the existence of *Portions of the preliminary work on this study were done during the first author's tenure as a predoctoral fellow under USPHS Fellowship IFlMll·30 630-01Al. Some equipment used in early stages was loaned under USPHS Grant NH 12120-02 to Eliot Hearst. I thank Robert S. Daniel, Irwin D. Nahinsky, and David Premack for helpful suggestions or comments during preliminary work on this study. 73 a single limbic pacemaker mechanism for a wide variety of rhythmic behavior patterns." Consider that if there were a single central pacemaker providing a time base for a variety of behaviors, that pacemaker would be expected to continue to run at least at all times whe...