IT IS ARGUED THAT THE INSANITY DEFENSE HAS DEGENERATED TO A LEGALISTIC PLOY IN MANY CASES, DOES NOTHING TO PROMOTE JUSTICE, DAMAGES RESPECT FOR LAW, SUSTAINS THE SHAM OF THE 'BATTLE OF THE EXPERTS' IN THE COURTROOMS, AND NEEDLESSLY INCREASES THE COST OF TRYING AND DEFENDING ALLEGEDLY MENTALLY DISORDERED CRIMINALS. EXAMININATION OF THE USE OF THE INSANITY DEFENSE IN THE CRIMINAL JUSTICE SYSTEM LEADS TO TWO CONCLUSIONS: (1) THERE IS NO MORALLY SOUND BASIS FOR SELECTING A MENTAL DISEASE OR DEFECT AS JUSTIFICATION FOR EXCULPABILITY WHILE EXCLUDING OTHER DETERMINANTS, SUCH AS HEREDITY, POVERTY, FAMILY ENVIRONMENT, AND CULTURAL DEPRIVATION; AND (2) THERE EXISTS NO SCIENTIFIC, EFFECTIVE MEANS OF DETERMINING THE DEGREE OF MENTAL DISEASE OR DEFECT IN SUCH A WAY THAT A DEFENDANT CAN BE FAIRLY FOUND TO BE LACKING IN CRIMINAL RESPONSIBILITY ON THAT ACCOUNT. ALSO TO BE CONSIDERED IS THE PROBLEM OF EARLY DISCHARGE FROM HOSPITALS OF INSANITY-ACQUITTED PERSONS WHO GO ON TO COMMIT FURTHER CRIMES. ANOTHER PROBLEM IS THE FEIGNING OF INSANITY TO AVOID PRISON SENTENCE. CONSTITUTIONAL ASPECTS OF ABOLISHING THE INSANITY DEFENSE ARE CONSIDERED. PARTICULAR REASONS FOR ABOLISHING THE INSANITY DEFENSE IN NEW YORK STATE ARE CITED. A BIBLIOGRAPHY IS INCLUDED. (LKM)