THE JURORS' PERCEPTIONS OF MENTAL ILLNESS ARE QUESTIONED, SINCE SUCH PERCEPTIONS ARE ESSENTIAL TO THE JURORS' DETERMINATION OF A DEFENDANT'S CRIMINAL RESPONSIBILITY. ONE OF THE SPECIAL COMPLEXITIES FOR THE JURY IN A DEFENSE OF INSANITY TRIAL IS THE TESTIMONY OF THE EXPERT WITNESSES, USUALLY PSYCHIATRISTS. THIS ARTICLE CITES CASES IN WHICH THE JURORS DID NOT ALWAYS FOLLOW THE ADVICE IMPLICIT OR EXPLICIT IN THE EXPERTS' TESTIMONY. ALTHOUGH THEY APPEARED TO UNDERSTAND THE TECHNICAL VOCABULARY AS WELL AS THE ESSENCE OF THE TESTIMONY, THEY CHOSE TO EXERCISE THEIR INDEPENDENT JUDGMENT ON A RATIONAL BASIS. WHILE ADMITTING THAT PROBABLY LESS THAN 2 PERCENT OF ALL CRIMINAL JURY TRIALS IN A GIVEN YEAR INVOLVE A DEFENSE OF INSANITY, THIS STUDY POINTS OUT THAT INSANITY DEFENSE TRIALS ATTRACT CONSIDERABLE ATTENTION FROM THE MASS MEDIA AND THE LEGAL PROFESSION BECAUSE OF THE COMPLEXITY AND SUBTLETY OF THE ISSUES SURROUNDING SUCH CASES. THE JURYS' PERFORMANCES ON THESE OCCASIONS PROVIDE A SEVERE TEST OF THE LAY PERSON'S COMPETENCE IN UNDERSTANDING AND RESOLVING JUDICIAL ISSUES. IN VIEW OF THE EVIDENCE PRESENTED, THE JURY'S TREATMENT OF THE ISSUES INVOLVED IN DEFENSE OF INSANITY TRIALS, INCLUDING ITS PERCEPTIONS OF THE LIKELY CONSEQUENCES OF A 'NOT GUILTY BY REASON OF INSANITY' VERDICT, HAS CONSISTENTLY INDICATED THE JURORS' COMPETENCE, RESOURCEFULNESS, AND WILLINGNESS TO FULFILL ITS RESPONSIBILITIES IN A MANNER CONSISTENT WITH THE RULES OF LAW AND EVIDENCE. TABULAR DATA AND ONE REFERENCE ARE INCLUDED. (LGR)