ALL METHODS EMPLOYED BY PROFESSIONAL LIE DETECTOR OPERATORS ARE PREDICATED ON THE BELIEF THAT THERE IS A DISTINCTIVE PATTERN OF PHYSIOLOGICAL RESPONSE ACCOMPANYING LYING WHICH CAN BE DISTINGUISHED FROM THE PATTERN ACCOMPANYING TRUTH-TELLING. MANY STUDIES INDICATE, HOWEVER, THAT PHYSIOLOGICAL RESPONSE PATTERNS VARY GREATLY FROM ONE INDIVIDUAL TO ANOTHER, ALLOWING LITTLE CREDENCE FOR THE BELIEF THAT ALL PERSONS CAN BE EXPECTED TO SHOW THE SAME CHARACTERISTIC PATTERN WHEN LYING AND DIFFERENT PATTERNS WHEN TELLING THE TRUTH. IN THIS EXPERIMENT, THE USE OF PHYSIOLOGICAL MEASUREMENTS TO DETECT, NOT LYING, BUT THE PRESENCE OF 'GUILTY KNOWLEDGE' IS EVALUATED. THE TECHNIQUE REQUIRES ONLY THE MORE REASONABLE ASSUMPTION THAT GUILTY PERSONS WILL SHOW SOME INVOLUNTARY PHYSIOLOGICAL RESPONSE (GSR) TO STIMULI RELATED TO REMEMBERED DETAILS OF THEIR CRIMES. EACH OF THE 20 SUBJECTS (INCLUDING MEDICAL STUDENTS, STAFF PSYCHOLOGISTS, AND SECRETARIES) WAS GIVEN A BRIEF LECTURE ON THE NATURE OF GSR, THE LIE DETECTOR IN GENERAL, AND THE PRINCIPLE OF THE GUILTY KNOWLEDGE METHOD. AFTER BEING ATTACHED TO THE GSR ELECTRODES, EACH SUBJECT WAS ALLOWED TO SIT BEFORE THE RECORDING INSTRUMENT AND TO PRACTICE PRODUCING VOLUNTARY GSR'S BY VARIOUS METHODS. EACH WAS TOLD WHAT THE FORMAT OF THE QUESTIONING WOULD BE, AND WAS CAUTIONED AGAINST ATTEMPTING TO DEFEAT THE TEST MERELY BY INHIBITING RESPONSES; EACH WAS ADVISED, CORRECTLY, THAT THE BEST WAY TO CONFUSE THE SCORING SYSTEM WOULD BE TO PRODUCE GSR'S OF VARIOUS AMPLITUDES TO THE INNOCENT ALTERNATIVES IN AS RANDOM A PATTERN AS POSSIBLE. SUBJECTS WERE OFFERED A PRIZE OF $10 EACH IF THEY COULD DEFEAT THE OBJECTIVE SCORING SYSTEM EMPLOYED. NO SUBJECT WAS ABLE TO DEFEAT THE SYSTEM; CORRECT CLASSIFICATION WAS OBTAINED IN 100 PERCENT OF THESE CASES WITHOUT AMBIGUITY, USING OBJECTIVE SCORING OF THE GSR PROTOCOL ALONE. FOOTNOTES, TABLES, AND REFERENCES ARE INCLUDED IN THE STUDY. (LWM)