Decision Support Systems (DSS) are designed to help human beings in solving problems more efficiently or making better decisions. While an increasing number of DSS have been and are developed, the effectiveness of such systems has not yet been demonstrated. This study proposes a conceptual framework for measuring the effectiveness of DSS and reports the results of a before-and-after study designed to compare two experimental groups of problem solvers assisted by one of two technologies for conflict resolution with a control group without any technology. The two technologies that are examined in this paper consist of a computerized DSS for conflict resolution, Resolve(!), and a videotape on conflict resolution, Video. Various measures of the problem solving episode were recorded, including both process and outcome measures. Overall, the groups with access to the technologies perceived a significantly better resolution of the problem they addressed than their control group counterpart. The two technologies differed essentially on two out of 11 variabales: subjects assigned to the computerized DSS technology generated more alternative solutions to the problem they tried to solve and reported a higher perceived progress in the resolution of the problem, than did subjects who were assigned to the videotape technology.