A HOMOGENOUS, 'NORMAL' SAMPLE WAS CHOSEN AFTER INTERVIEWING AND DIAGNOSTIC TESTING OF A LARGE GROUP OF VOLUNTEER MALE COLLEGE STUDENTS. HALF OF THE SUBJECTS WERE RANDOMLY ASSIGNED TO ROLE-PLAY PRISON GUARDS FOR 8 HOURS EACH DAY, WHILE THE OTHER ROLE-PLAYED INMATES INCARCERATED FOR NEARLY (1) FULL WEEK. DURING THE STUDY, THE 'PRISONER' SUBJECTS REMAINED IN A MOCK PRISON BUILT IN A 35-FOOT SECTION OF A BASEMENT CORRIDOR IN THE STANFORD UNIVERSITY PSYCHOLOGY BUILDING AND CONSISTING OF A SOLITARY CONFINEMENT FACILITY (2X2X7 FEET) AND THREE CELLS (6 X 9) WITH A COT SERVING AS THE ONLY FURNITURE. NEITHER GROUP RECEIVED ANY SPECIAL TRAINING IN THEIR ROLES. CONTINUOUS, DIRECT OBSERVATION OF BEHAVIORAL INTERACTIONS WAS SUPPLEMENTED BY VIDEO-TAPED RECORDING, QUESTIONNAIRES, SELF-REPORT SCALES, AND INTERVIEWS. THESE DATA SOURCES INDICATED THAT THE SIMULATED PRISON ENVIRONMENT DEVELOPED INTO A PSYCHOLOGICALLY COMPELLING CONFINEMENT. AS SUCH, IT ELICITED INTENSE, REALISTIC, AND OFTEN PATHOLOGICAL REACTIONS FROM MANY OF THE PARTICIPANTS. THE INMATES EXPERIENCED A LOSS OF PERSONAL IDENTITY AND THE ARBITRARY CONTROL OF THEIR BEHAVIOR, WHICH RESULTED IN A SYNDROME OF PASSIVITY, DEPENDENCY, DEPRESSION, AND HELPLESSNES. IN CONTRAST, THE GUARDS EXPERIENCED A MARKED GAIN IN SOCIAL POWER, STATUS, AND GROUP IDENTIFICATION. SOME OF THE INMATES DEVELOPED ACUTE EMOTIONAL DISTURBANCE SEVERE ENOUGH TO WARRANT EARLY RELEASE. AT LEAST A THIRD OF THE GUARDS BECAME FAR MORE AGGRESSIVE AND DEHUMANIZING TOWARD THE INMATES THAN WOULD ORDINARILY BE PREDICTED IN A SIMULATION STUDY. FEW OF THE OBSERVED REACTIONS COULD BE ATTRIBUTED TO PERSONALITY TRAIT DIFFERENCES EXISTING BEFORE THE SUBJECTS ASSUMED THEIR ASSIGNED ROLES. TABULAR DATA AND REFERENCES ARE PROVIDED. (AUTHOR ABSTRACT MODIFIED--RCB)