A TOTAL OF 720 SUBJECTS, 221 FEMALES AND 499 MALES, PARTICIPATED PRIMARILY AS PART OF A CLASS EXERCISE FOR AN INTRODUCTORY SOCIAL PSYCHOLOGY COURSE. OF THE TOTAL SAMPLE, 647 PERSONS WERE RANDOMLY ASSIGNED TO JURIES AND EXPERIMENTAL CONDITIONS AND THE REMAINING 73 PERSONS WERE ASSIGNED TO INDIVIDUAL CONDITIONS. FACTORS INVOLVED IN THE STUDY DESIGN WERE THE SIZE OF THE MOCK JURY (6 OR 12 PERSONS) AND THE ASSIGNED DECISION RULE (UNANIMOUS DECISION OR TWO-THIRDS MAJORITY DECISION). AT EACH EXPERIMENTAL SESSION, SUBJECTS WERE ASSEMBLED IN LARGE CLASSROOMS, ASSIGNED TO VARIOUS EXPERIMENTAL CONDITIONS, AND THEN CONDUCTED TO SMALLER EXPERIMENTAL ROOMS WITH ONE JURY TO A ROOM. AUDIOTAPED INSTRUCTIONS WERE PLAYED SIMULTANEOUSY TO EVERYONE. QUESTIONNAIRES WERE FILLED OUT BY BOTH EXPERIMENTAL AND INDIVIDUAL CONTROL SUBJECTS TO INDICATE JURY OUTCOME, EXCEPT THAT QUESTIONS DEALING WITH SOCIAL INTERACTION WERE OMITTED FOR THE INDIVIDUAL CONTROLS. THE SELECTION OF A FOREMAN AND JURY DELIBERATION WERE DELETED FROM PROCEDURES USED FOR THE INDIVIDUAL CONTROLS; THEY REFLECTED PERSONALLY ON THE EVIDENCE RATHER THAN DELIBERATING IN A JURY MANNER. NEITHER ASSIGNED RULE NOR JURY SIZE HAD A SIGNIFICANT EFFECT UPON VERDICT DISTRIBUTION, BUT AVERAGE DELIBERATION TIME AND THE NUMBER OF POOLS WERE SIGNIFICANTLY INFLUENCED. INDIVIDUALS GAVE A SLIGHTLY HIGHER PROPORTION OF GUILTY VERDICTS THAN JURIES. A TWO-THIRDS MAJORITY SOCIAL DECISION MODEL BEST PREDICTED OVERALL VERDICT DISTRIBUTION. THE NEED FOR BOTH THEORETICAL AND EMPIRICAL RESEARCH ON JURIES IS STRESSED. SUPPORTING DATA ARE TABULATED, BUT THE QUESTIONNAIRES ARE NOT INCLUDED. A LIST OF REFERENCES IS PROVIDED, WITH INFORMATION ON PROCEDURAL ASPECTS OF THE EXPERIMENT APPENDED. (DEP)