In order to test the concept of "sleep learning" cats were exposed to habituation treatment of auditory stimuli during different stages of the sleep-waking cycle. While it was possible to demonstrate that habituation to an auditory stimulus can take place in paradoxical sleep (PS) and slow-wave sleep (SWS) as well as during periods of wakefulness, it was not always possible to demonstrate a transfer of habituation from the training period to other periods. A complete transfer of habituation occurred between the two sleep periods (PS and SWS); a partial transfer of habituation occurred between the waking period and both of the two sleep stages (PS and SWS), but only a minimal transfer of habituation was found between any one of the sleep stages and the waking period. When the cats were able to transfer the habituation, they also were able to discriminate between the habituating tone and a novel tone. The findings that only minimal transfer of habituation could occur between each of the sleep stages and the waking period do not lend support to the concept of "sleep learning"