The effect of working unconventional hours, i.e. afternoon, night, and rotating shifts, on the psychological and physiological well being of workers is investigated. Data from 1,200 nurses and a similar number of food processors were collected by review of health and accident files and by administration of a lengthy questionnaire. Areas of inquiry included: basic subject demography, incidence and prevalence of physical complaints, illness histories, eating patterns, sleep patterns, medication usage, lifestyle and domestic patterns, and psychological profiles. Findings confirm studies of European shift workers that demonstrate a significantly greater difficulty in adapting to work schedules experienced by all shift workers other than day shift workers. Rotating shift workers, i.e. those who not only work at unconventional hours but who also move from shift to shift, clearly encounter the most difficulty in adjusting their psychobiological rhythms and patterns to their work schedules. These data suggest that shift work may pose a distinct health hazard for certain rotating shift workers.