Investigated whether paradoxical sleep is implicated in the storage of information acquired during shuttle-box avoidance. Wistar rats were given 5 brief training sessions distributed over the light period of the diurnal cycle. During the intervals between sessions the animals were selectively deprived of paradoxical sleep by awakening them every time they showed this type of sleep. The onset of paradoxical sleep was identified when hippocampal theta rhythm occurred during behavioural sleep. Yoked control animals got the same treatment irrespective of their sleep-waking behaviour, whereas free sleep rats were allowed to sleep undisturbed. In spite of large differences in the amount of paradoxical sleep during the intersession intervals no differences in learning performances were found among the groups. A tendency toward more intertrial crossings was noted in the paradoxical sleep deprived group at the end of training. It is concluded that storage of information acquired during distributed shuttle-box avoidance is not dependent on the presence of paradoxical sleep immediately following learning. Some possibilities are considered that paradoxical sleep may still be involved in memory storage processes.