Because many drug users have diverse problems that contribute to their drug abuse, rehabilitation programs are needed that focus on changing the behavior and attitudes of persons addicted to drugs. One approach is marathon group therapy, which should last at least 16 continuous hours and allow members to express their feelings, explain personal problems, and gain insight into their behavior toward other people. Participants in this study were all males with extensive histories of illicit drug use. The group was equally divided between blacks and whites, and most were about 23 years old. The residential drug program provided counseling, life skills classes, educational classes, and recreational activities for inmates, but did not allow them to work at a job. Volunteers were selected and randomly divided into a group of 12 that participated in the marathon therapy and a control group of 16 who received no treatment. The group facilitators were two full-time drug abuse counselors from the center and a counseling psychologist who worked part-time in the program. During the 16-hour marathon session, facilitators encouraged residents to reveal their problems and provide one another with constructive feedback. By the end of the therapy, the participants expressed satisfaction with the group's achievements and positive feelings toward one another and the facilitators. Both the control and experimental groups completed posttests that used the semantic differential technique to assess the meaning of the following concepts to participants: kindness, reality, the future, anger, guilt, my real self, drug treatment programs, counselors, counseling, and group counseling. Analysis of the test data showed that inmates who participated in the marathon session responded higher on the group counseling subscale and lower on the guilt subscale than the control group members. These findings support previous research which indicated that marathons can improve clients' perceptions of group counseling and thus increase its effectiveness. A table of test scores and 27 references are included.