Voluntary participants were 240 male inmates who had been convicted of aggravated crimes, defined as offenses committed against other human beings with the intent to cause bodily harm. Three of the 61 prison units in Texas housing male inmates were selected as sites for the study. The Buss Perry Aggression Inventory and the Profile of Mood States-Short Form were the two psychometric instruments used in the study; 202 of the 240 participants completed the psychometric instruments. The measures of verbal aggression, hostility, and anger showed a decrease in these variables in the weight-training group; whereas, vigor scores significantly decreased in the non-weight-training group. An analysis of the findings suggests that participation in any voluntary physical activity may act as a catharsis for an inmate, thereby contributing to a decrease in aggression levels. Because no causality can be claimed from this study, further research should be conducted. The time frame of the current study should be expanded, and outside variables should be controlled. Qualitative methods of data gathering also are recommended. 2 tables, 5 figures, a copy of the Buss Perry Aggression Inventory, and 37 references