The rationale, design, and operation of the Perceptronics' Group Decision Aid, are described, and some experimental studies of its effectiveness are reported. The decision aid is supported by a PDP 11/45 minicomputer using the UNIX operating system. It features simple individual data entry terminals and a large screen (7 ft) color video display for feedback of computer-generated information. The system's purpose is to guide the group decisionmaking process by selective elicitation of a decision tree which incorporates value and probability inputs from all group members. Conflicts in value judgments are identified and discussions are initiated through use of multiattribute utility analysis. A specially trained system operator, called an intermediator, facilitates group interaction with the aiding program so that group members need have no prior familiarity with computers or decision analysis. Experimental studies are described comparing the performance, behavior, and responses of aided and nonaided groups in a complex international crisis decision problem. Improvements with aiding were noted in the completeness of the decision process and in the satisfaction and confidence of the group participants.