In order to further assess the validity of the competing response measure as an index of learning and memory abilities in young -mice, three groups of mice under different response-reinforcement contingencies received consecutive daily 25-trial sessions on a straight-alley shock-escape task beginning at 7 days of age. In the first group, shock offset was contingent upon reaching the goal end of the alley on each trial. Each mouse in the second group received identical amounts of shock and handling on each trial as a littermate in the first group, but shock offset was not contingent upon reaching the goal for members of this group. Mice in a third group also began test sessions yoked to littermates in the first group, but were unyoked on the day following that on which their littermate achieved a criterion performance of a 50% reduction in competing responses from one session to the next. On all following days, shock offset was contingent upon reaching the goal on each trial. The results support earlier research suggesting that 24-h memory of escape training develops at about 9 days of age for this task, and demonstrate that changes in competing responses due to maturation and/or age-dependent differences in shock sensitivity can be separated from those due to learning/memory functions .In a recent paper reviewing literature on the -ontogeny of learning and memory in lower animals, Campbell and Coulter (1976) point out that remarkably few experiments have been related to the acquisition by very young organisms of basic response-reinforcement contingencies characteristic of simple approach or escape tasks . They state further that this paucity of studies may be due to the fact that learning by adult subjects on these tasks is typically assessed in terms of response speed, a measure which may place the immature animal at a disadvantage.Over the past 7 years, research from our laboratory, as well as that from Misanin's lab at Susquehanna University , has examined the development of acquisition and memory processes by neonatal and infant mice and rats using a simple straight-alley shock-escape task. As suggested by Campbell and Coulter (I 976). our research has clearly indicated that the running speed measure is , at best, inconsistent in reflecting improved escape behavior over a training session for rats (e .g.