A REVIEW OF THE LITERATURE SHOWS THAT A CONTROL GROUP OR DOUBLE-BLIND DESIGN HAS BEEN USED RARELY IN DIPHENYLHYDANTOIN STUDIES, BUT THIS TYPE OF DESIGN HAS PROVED EFFECTIVE. CONSEQUENTLY, THE PRESENT STUDY OF BERKSHIRE FARM, N.Y., INMATES EMPLOYED A DOUBLE-BLIND DESIGN. FOLLOWING A PILOT STUDY INVOLVING 4 SUBJECTS FOR 7 DAYS, STAFF SELECTED BOYS FROM 10 COTTAGES USING THE FOLLOWING BEHAVIORS AS CRITERIA FOR INCLUSION: ANGER, ERRATIC PERFORMANCE, HYPERACTIVITY OR IMPULSIVITY, IRRITABILITY, POOR CONCENTRATION, AND SLEEPLESSNESS. ON THE BASIS OF DISRUPTIVE BEHAVIOR SCORES, 25 COHORT PAIRS WERE FORMED. THE GROUPS WERE ASSIGNED TO TWO TREATMENT CONDITIONS AND TOLD THEY WOULD BE TAKING MEDICATION FOR AN INDEFINITE PERIOD. FOR 76 DAYS, THE 2 GROUPS TOOK 2 CAPSULES DAILY OF 100 MILIGRAMS OF DIPHENYLHYDANTOIN OR OF A PLACEBO. ASSESSMENTS WERE PERFORMED BEFORE AND AFTER THE MEDICATION PERIOD, USING TEST BATTERIES CONSISTING OF PSYCHIATRIC EVALUATION PROFILES, THE JUNIOR-SENIOR HIGH SCHOOL PERSONALITY QUESTIONNAIRE, PICTURE RATING TECHNIQUES, THE PORTEUS MAZE TEST, EXTENSION AND SUPPLEMENT TESTS, THE KATZ ADJUSTMENT SCALE, AGGRESSIVENESS TESTS, THE GRAPHIC IMPULSIVITY SCALE, CLASSROOM BEHAVIOR INVENTORIES, BRIEF PSYCHIATRIC RATING SCALES, AND SCHOOL CONDUCT REPORTS. RESULTS OF SCALE SCORES ANALYSES SHOW THAT DIPHENYLHYDANTOIN UNDER CONTROLLED CONDITIONS DID NOT ACT AS PREDICTED. THE PLACEBO GROUP EVINCED A SIGNIFICANT MITIGATION OF DISTRESS, UNHAPPINESS, NEGATIVISM, AGGRESSIVENESS, DISTRUST, SLEEPLESSNESS, VERBAL EXPANSIVENESS, AND IRRITABILITY. THE PRETREATMENT, POSTTREATMENT, AND FOLLOWUP MEAN SCORES ARE SIGNIFICANT SINCE THEY REVEAL MARKED DIMINUTION IN DISRUPTIVE BEHAVIOR FOR BOTH GROUPS FROM THE BEGINNING OF TREATMENT TO 30 DAYS AFTER ITS TERMINATION. TABULAR STUDY DATA AND REFERENCES ARE PROVIDED. (DAG)