Abstract
The extension of man's working environment and its control have lead to a new consideration of his “normal“ neuro-physiological and psychological rhythms. There are some fifty such patterns of fluctuating functions within man which have various degrees of influence upon his level of performance and ability to maintain performance. Data are provided from physiological and psychological research in an attempt to provide perspective for selection of appropriate personnel and establishment of work/rest or duty cycles in deference to these influences.