In the first stage of this research, several relevant literature reviews were conducted. One review dealt with the ability to focus attention for long periods of time addressed two topics: sustained attention and the effects of physical conditions in the working environment; and the effect of human physical circumstances on long-lasting sustained attention and performance. A second review disscussed methods of measuring vigilance in the field, focusing on phsiological correlates that enable quantifying human fatigue. The last review focused on the characteristics and problems of working in shifts, and recommended shift distributions on a weekly and daily basis in order to minimize these difficulties. In addition, we administered questionnaires to all shift-workers in an organization that employs multiple shift distribution systems. This section of the study aimed to draw conclusions regarding the fatigue level of the workers and to obtain evidence about shift distribution systems that can potentially reduce fatigue. A simple, brief cognitive test was developed for the second part. This test was administered once every half hour to a small group of participants as they performed a long sustained-attention task. The goal was to pinpoint decreases in performance levle in the cognitive test that would correspond with a reduction in their performance on the sustained-attention task.