A TOTAL OF 180 JURORS FROM THE KINGS COUNTY, NEW YORK, JURY ASSEMBLY ROOM SERVED AS MOCK JURORS IN A MURDER TRIAL PRESENTED ON VIDEOTAPE. SUBJECTS WERE RANDOMLY ASSIGNED TO CELLS OF A TWO BY TWO DESIGN WHICH VARIED JURY SIZE (6 VS. 12) AND VERDICT DECISION RULE (MAJORITY VS. UNANIMOUS). THAT IS, SUBJECTS WERE ASSIGNED TO ONE OF THE FOUR FOLLOWING CONDITIONS: (1) 12-MEMBER JURIES, UNDER A UNANIMOUS DECISION RULE; (2) 12-MEMBER JURIES, UNDER A MAJORITY DECISION RULE; (3) 6-MEMBER JURIES, UNDER A UNANIMOUS DECISION RULE; OR (4) 6-MEMBER JURIES, UNDER A MAJORITY DECISION RULE. AN ANALYSIS OF VARIANCE SHOWED THAT JURY VERDICTS BECAME MORE SEVERE AS A RESULT OF DELIBERATING IN THE SMALLER JURY AND UNDER MAJORITY RULE. THE MAJORITY DECISION RULE CLEARLY RESULTED IN MORE CONVICTIONS. EMPIRICAL SUPPORT FOR THE SMALLER SIZE JURY EFFECT WAS LIMITED, AS THE COURT WITHDREW PERMISSION FOR THE RESEARCH AFTER A TOTAL OF ONLY 20 JURIES WERE TESTED. (AUTHOR ABSTRACT MODIFIED.)