Learning material was presented to independent groups of subjects either after arousal from non-Rapid Eye Movement (non-REM) sleep, after arousal from REM sleep, or under conditions of no prior sleep. Measures of immediate and subsequent free recall were taken. Memory performance was found to be impaired where learning took place after non-REM arousal. This was manifest in the number of categories recalled, over both immediate and subsequent recall, and in the number of items recalled per category over subsequent recall. It was suggested that the memory performance decrement after non-REM arousal may be understood in terms of a retrieval deficit as well as a coding deficit. It is possible that the former is consequent upon a lower general level of arousal, whereas the latter is specific to memory.