Since its establishment in 1973, only 2 assaults and 7 serious incidents have occurred. The psychological characteristics and criminal histories of prisoners in the unit are described, and a quantitative account is given of their responses to the regime. The intrinsic and situational factors that produce the changes in behavior associated with the Special Unit are identified, and explanations as to why these factors account for these changes are explored. 2 tables, 2 figures and 41 references. (Author abstract modified)