Infants engage in an extraordinary amount of learning during their waking hours even though much of their day is consumed by sleep. What role does sleep play in infant learning? Fifteen-month-olds were familiarized with an artificial language 4 hr prior to a lab visit. Learning the language involved relating initial and final words in auditory strings by remembering the exact word dependencies or by remembering an abstract relation between initial and final words. One group napped during the interval between familiarization and test. Another group did not nap. Infants who napped appeared to remember a more abstract relation, one they could apply to stimuli that were similar but not identical to those from familiarization. Infants who did not nap showed a memory effect. Naps appear to promote a qualitative change in memory, one involving greater flexibility in learning.