SUBJECTS RECEIVED BOOKLETS OUTLINING A SITUATION IN WHICH THE VICTIM WAS RAPED AFTER HAVING MET THE DEFENDANT AT A DANCE AND LEAVING WITH HIM VOLUNTARILY. MEDICAL EVIDENCE CONFIRMED THE CONTENTION OF FORCIBLE RAPE. FOUR CONDITIONS WERE USED: HIGH/LOW AMBIGUITY PLUS INSTRUCTION/NO INSTRUCTION, WITH 6 MALES AND 6 FEMALES PER CONDITION. IN THE LOW AMBIGUITY CONDITION, INDEPENDENT WITNESSES AFFIRMED THE IDENTITY OF THE DEFENDANT AND THE DEFENDANT MERELY ALLEGED THAT HE HAD RETURNED THE VICTIM TO HER HOME AND WAS INNOCENT. IN THE HIGH AMBIGUITY CONDITION, THE VICTIM DISPLAYED HESITATION IN HER IDENTIFICATION OF THE DEFENDANT AND THE DEFENDANT'S ALIBI WAS SUBSTANTIATED BY HIS GIRLFRIEND BUT CONTRADICTED BY HIS LANDLADY. IN THE INSTRUCTION CONDITION, THE JUDGE INSTRUCTS THAT EVIDENCE SUGGESTING AN ASSUMPTION OF RISK ON THE PART OF VICTIM SHOULD NOT AND LEGALLY CAN NOT INFLUENCE THE JUROR'S JUDGEMENT OF DEFFENDANT GUILT OR INNOCENCE. FOLLOWING COMPLETION OF A MEASURE OF INDIVIDUAL JUDGEMENT OF DEFENDANT AND VICTIM RESPONSIBILITY AND CERTAINTY OF VERDICT JUDGEMENT (GUILTY/NOT GUILTY), SUBJECTS WERE ASSIGNED TO MIXED-SEX FOUR PERSON GROUPS FOR 15 MINUTES OF DISCUSSION DURING WHICH THEY WERE TO REACH A UNANIMOUS VERDICT AND SENTENCE. FACTORIAL ANALYSIS OF VARIANCE INDICATED THAT LEVEL OF AMBIGUITY DID NOT INFLUENCE INDIVIDUAL VERDICTS, FEMALES EXPRESSED GREATER CERTAINTY OF VERDICT JUDGEMENTS AND ATTRIBUTED MORE RESPONSIBILITY (BLAME) TO THE DEFENDANT THAN DID MALES. THE PRESENCE OF INSTRUCTIONS RESULTED IN INCREASED LENGTH OF SENTENCE. A SIGNIFICANT SEX/AMBIGUITY INTERACTION WAS ALSO FOUND: MALES ATTRIBUTED MUCH GREATER RESPONSIBILITY TO THE DEFENDANT UNDER THE LOW AMBIGUITY CONDITION THAN UNDER THE HIGH AMBIGUITY CONDITION, WHILE FEMALES ASCRIBED SOMEWHAT GREATER RESPONSIBILITY TO THE DEFENDANT UNDER HIGH AMBIGUITY THAN UNDER LOW AMBIGUITY. MALES TENDED TO BLAME THE VICTIM MORE UNDER HIGH AMBIGUITY THAN UNDER LOW AMBIGUITY, WHILE LEVEL AMBIGUITY HAD LESS EFFECT ON FEMALES' ATTRIBUTIONS OF VICTIM RESPONSIBILITY. GROUP DISCUSSION DID NOT INFLUENCE CERTAINTY OF VERDICT, BUT DID INFLUENCE THE LENGTH OF SENTENCE IN THE DIRECTION OF MORE LENIENT SENTENCING. SEX DIFFERENCES FOUND SUGGEST THAT JUDGEMENTS OF GUILT MAY BE ROOTED IN CONTRASTING DEFENSIVE REACTIONS OF MALES AND FEMALES TO RAPE, AND ARE CONSISTENT WITH THE HYPOTHESIS THAT SUBJECTIVE FACTORS ARE CONSIDERED IN THE JUDICIAL DECISIONMAKING PROCESS TO THE EXTENT THAT THE EVIDENCE PRESENTED IS INCONCLUSIVE. REFERENCES ARE INCLUDED. (JAP)