POLYGRAPH EVIDENCE IS GENERALLY EXCLUDED FROM U.S. COURTS BECAUSE IT MAY UNDULY INFLUENCE JURIES. THIS ARTICLE DESCRIBES AN EXPERIMENT WHOSE AIM WAS TO PRESENT TO DIFFERENT JURIES (1) A CASE WITHOUT POLYGRAPH TESTIMONY, (2) THE SAME CASE WITH ADDED POLYGRAPH EVIDENCE FAVORABLE TO THE ACCUSED, AND (3) THE SAME CASE WITH POLYGRAPH EVIDENCE UNFAVORABLE TO THE ACCUSED. TWELVE MOCK JURIES WERE RUN USING UNIVERSITY PSYCHOLOGY STUDENTS WHOSE MEAN AGE WAS 22.7 YEARS. WITHOUT POLYGRAPH EVIDENCE, THERE WERE 31-PERCENT DECISION CHANGES FROM PREDELIBERATION TO FINAL DECISION; WITH UNFAVORABLE POLYGRAPH EVIDENCE, ONLY 7.3 JURORS CHANGED DECISIONS; AND WITH FAVORABLE EVIDENCE, ONLY 13.1 PERCENT MADE DECISION CHANGES. CONTROLLED INTRODUCTION OF POLYGRAPH RESULTS UNFAVORABLE TO THE ACCUSED THUS HAD SIGNIFICANT IMPACT ON THE JUROR'S DECISONMAKING COMPARED TO THE INTRODUCTION OF NO POLYGRAPH INFORMATION. ALTHOUGH POLYGRAPH EVIDENCE HAD A IMPACT ON DECISIONMAKING, IT APPEARED TO DO SO WITHOUT THE CONSCIOUS AWARENESS OF MOST JURORS, AS GROUP DISCUSSIONS INDICATED. FURTHER RESEARCH IS REQUIRED TO COMPARE THE EFFECTS OF ADDITIONAL POLYGRAPH TESTIMONY TO ADDITIONAL OTHER TESTIMONY; THE EFFECTS OF POLYGRAPH EVIDENCE CONFLICTING WITH OTHER EVIDENCE; THE EFFECTS OF VARIATION IN DEGREE OF RELIABILITY; AND EFFECTS IN DIFFERENT TYPES OF CASES. FOOTNOTES ARE GIVEN. (MJW)