• METHODS Data were obtained from a random sample of critical care nurses in the United States. Nurses eligible for the study were mailed two 14-day logbooks to fill out. Information collected included the hours worked, the time of day worked, overtime hours, days off, and sleep-wake patterns. On days worked, the respondents completed all work-related questions and questions about difficulties in remain- ing awake while on duty. Space was provided for descriptions of any errors or near errors that might have occurred. On days off, the nurses completed only those questions about sleep-wake patterns, mood, and caffeine intake.