This paper discusses factors related to negative psychological and physiological reactions (i.e., violent deaths, psychiatric commitments, self-mutilations, attempted suicides, disciplinary infractions, etc.) to life in institutional environments such as prisons, schools, off-shore oil rigs, and homes for the aged. Factors discussed are: (1) social density--number of individuals living in a sleeping area; (2) spatial density--space per person; and (3) unit population--population in total living unit. The hypothesis is that negative reactions to crowding can best be understood by evaluating these factors in light of the nature and degree of their disruption (social disorganization) in various institutional environments. Data on crowding behavior of rats, monkeys, and human subjects were examined in order to test this notion of the importance of the role of social disorganization. A wide variety of cases was examined, including studies based on entry into a dormitory in which friendship patterns were already established, assignment to a new unit, high turnover rates, replacement of highly dominant members in a living group by other highly dominant individuals, removal of partitions in rat cages, and rapid influx of strangers into a formerly cohesive group. Findings indicated that increased social disorganization in all cases studied resulted in increased stress and that increased stress in turn contributed to an increase in negative reactions. The conclusion is that the degree of social disorganization is positively related to the degree of observed negative effects associated with crowded housing conditions. (DB)