Summary: Sixteen male subjects slept in the laboratory for 4 consecutive nights. Night 1 was an adaptation night and night 2 waS a baseline night of uninterrupted sleep. On nights 3 and 4 subjects were asked to complete "intelligence" tests prior to sleep. One half of the subjects attempted to complete difficult versions of "intelligence" tests without knowing that they could not be completed in the time allotted. The other subjects were given easier versions of the same tests that they were able to complete in the time allotted. Night 3 was a night of uninterrupted sleep and night 4 involved REM period awakenings for the purpose of dream collection. Stressful manipulation consisted of telling the subjects before the administration of either set of tests that an average university student should complete most of the items within the allotted time. On night 3 both groups showed a significant increase in sleep latency and a significant decrease in REM density compared to the baseline night. On night 4 subjects in the difficult condition experienced significantly more anxiety in their dreams and somewhat higher levels of incorporation of the presleep material than subjects in the easy condition. Our findings suggest that following a stressful experience uninterrupted sleep has more short term adaptive value than a procedure which enhances dream recall and that subjects who incorporate elements from a presleep stressful event into their remembered dreams show less adaptation on awakening than subjects who do not. Key Words: Adaptation-Pre-and postsleep anxiety-Stress.In recent years a host of studies have focused on the interplay between waking and sleeping lives. Most studies have examined the effects of a large variety of artificially induced and naturally occurring presleep stressful events on the physiology of sleep and/ or dream content and dream affect (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Although the results have not been very consistent from study to study, the observed effects include increases in the latency to sleep onset, decreases in latency to REM sleep, decreases in the percentage of REM sleep, changes in dream affect, and incorporation of stressful elements into dreams.Some of these studies (7,8,12,13) have asked the additional question of how events during sleep affect subsequent waking experience. Greenberg et al. (12) presented a stressful film to three groups of subjects before they went to sleep and again in the morning. During the night one group of subjects was deprived of REM sleep, another was awakened during NREM sleep, and the third group was allowed to sleep without interruption. The REM-

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