The objective of this course is to give students the most up-to-date information on the biological, personal, and societal relevance of sleep. Personal relevance is emphasized by the fact that the single best predictor of daytime performance is the quality of the previous night's sleep. The brain actively generates sleep, and the first third of the course will overview the neurobiological basis of sleep cycle control. Sleep will be used as a vehicle for teaching basic neuroanatomical and neuropharmacological principles. This information will provide a cellular-level understanding of how sleep deprivation, jet lag, and substances such as alcohol, caffeine, and nicotine alter sleep and wakefulness. It is now clear that sleep significantly alters physiology. The second third of the class will cover sleep-dependent changes in physiology and sleep disorders medicine. Particular emphasis will be place on disorders of excessive sleepiness, insomnia, and sleep-dependent changes in autonomic control. Chronic sleep deprivation impairs immune function and promotes obesity. Deaths due to all causes are most frequent between 4 and 6 a.m., and the second portion of the class will highlight the relevance of sleep for preventive medicine. The societal relevance of the sleep will be considered in the final portion of the class. In an increasingly complex and technologically oriented society, operator-error by one individual can have a disastrous negative impact on the public health and safety. Fatigue-related performance errors contributed to the Three Mile Island and Chernobyl nuclear power plant failures and to the Exxon Valdez Alaskan oil spill. The personal relevance of fatigue-related performance errors will be considered by reviewing the recent data showing that in the U.S. more people die from medical mistakes each year than from highway accidents, breast cancer, or AIDS. Fulfillment of course objectives will be quantified by pre- versus post-class informational self-evaluation. In-class arousal levels will be facilitated by seminar participation.