An experimental group of 36 male work-release residents (mean age 29.44 yrs) participated in a 16-hr intervention program designed to enhance psychological maturity. Comparisons of the experimental Ss with a nonparticipant control group of 37 Ss (mean age 25.24 yrs) and with itself at pre- and posttesting (22 experimental and 24 control Ss) revealed significant changes on a number of psychological measures (e.g., a psychopathic state inventory; a self-attitude inventory; the Brief Symptom Inventory; an internal, powerful others, and chance control scale) favoring the experimental group. At pretesting, there were no significant differences between the experimental and control groups, but they differed at posttesting. Impulsivity, hostility, and anxiety were significantly lower in the experimental Ss, and they attributed significantly less mean control over their lives to luck and to powerful others and more to their own internal determination. The experimental Ss had also an increase in self-esteem. Implications for prison intervention and assessment methodologies are noted. (10 ref) (PsycINFO Database Record (c) 2016 APA, all rights reserved)