THE NATURE AND SCOPE OF THE INSANITY DEFENSE ARE CONSIDERED, ALONG WITH STATE PRACTICES IN ALLOCATING THE BURDEN OF PROOF ON THE ISSUE OF INSANITY, AND PERTINENT SUPREME COURT PRECEDENTS ON THE CONSTITUTIONAL SIGNIFICANCE OF THE RELATIONSHIP BETWEEN SANITY AND MENS REA. ANALYZED ARE THE COURT'S DECISIONS IN RE WINSHIP (1970) AND MULLANEY V. WILBUR (1975) WHICH STATED THAT THE DUE PROCESS CLAUSE REQUIRED THE PROSECUTION TO PROVE BEYOND A REASONABLE DOUBT EVERY FACT NECESSARY TO CONSTITUTE THE CRIME CHARGED. THE NOTE CONCLUDES THAT, TO THE EXTENT THAT ALLOCATING THE BURDEN OF PROOF OF INSANITY TO THE DEFENDANT COMPELS HIM TO DISPROVE FACTUAL ELEMENTS THAT ARE ALSO CRUCIAL TO THE MENS REA REQUIRED FOR THE CRIME, THE PRACTICE IS CONSTITUTIONALLY IMPERMISSIBLE. ONLY WHEN PROOF OF THE ELEMENTS OF INSANITY AS DEFINED BY THE STATE IS NOT INCONSISTENT WITH THE DEFENDANT'S CAPACITY TO ENTERTAIN THE STATUTORILY REQUIRED STATE OF MIND MAY THE STATE SHIFT THE BURDEN OF PROVING INSANITY TO THE DEFENDANT. EVEN IN SUCH CASES, INSTRUCTIONS MUST BE CAREFULLY DRAWN TO ENSURE THAT THE JURY IS NOT CONFUSED AS TO THE PROSECUTION'S DUTY TO PROVE MENS REA BEYOND A REASONABLE DOUBT. (AUTHOR ABSTRACT MODIFIED)