This paper discusses two studies undertaken to investigate the effects of population concentrating on the behavior of human subjects. Particular attention was paid to the space and interpersonal contact dimensions, over time, within a prison setting. Mood state self-reports and the rate of psychosomatic illness complaints were used to determine if inmate volunteers were sensitive to variations in crowding. The findings of these field studies parallel those reported in laboratory studies of crowding: no strong influence of variations in crowding was found. The mood and illness factors, although related to stress in other contexts, did not indicate reliable relationships with variations in crowding. (SJL)