The clients attended one 90-minute group session weekly. Direct confrontation was encouraged in the groups but was monitored by the group leaders. Topics of discussion addressed not only substance abuse recovery but also employment, financial, health, and relationship issues. The intent of the group sessions was to clarify the clients' problems, develop alternative solutions, examine possible consequences, and then use group support in experimentation with new behaviors. Group therapy was ongoing and continued as long as the client remained under intensive supervision. The study found that probationers with drug problems who received group therapy performed significantly more positive behaviors over a 12-month follow-up period than did otherwise similar controls, but no difference was found in the number of negative behaviors. It was also found that probationers with alcohol problems who received group therapy performed significantly more positive and fewer negative behaviors than otherwise similar controls. The study determined that there was no difference in the number of positive or negative behaviors between the drug abusing probationers who received group therapy and the alcohol abusing probationers who received group therapy. Recommendations are offered for future related research. 7 tables and 30 references