THE PAIRS WERE SELECTED SO THAT AT LEAST ONE PARTNER HAD ACTED OUT AS DELINQUENT OR CRIMINAL. IN 11 OF THE 15 PAIRS BOTH PARTNERS HAD BEEN INVOLVED IN A DELINQUENT OR CRIMINAL ACT (CONCORDANCE). IN THE REMAINING FOUR CASES, ONLY ONE PARTNER HAD COMMITTED SOME JUVENILE OFFENSE (DISCORDANCE). OF THE 11 CONCORDANT PAIRS, 6 WERE FOUND TO BE REPEAT OFFENDERS OF THE CHRONIC TYPE; THEY WERE CONSIDERED TO POSSESS PREDETERMINED DISPOSITIONS TOWARD CRIMINALITY. FOUR OTHER CONCORDANT PAIRS SHOWED DELINQUENT BEHAVIOR OF A MUCH LESS DISTURBING KIND, WHILE THE REMAINING PAIR SEEMED TO BE SCHIZOPHRENICS OF HEBEPHRENIC TYPE. IN THREE OF THE FOUR DISCORDANT PAIRS, DELINQUENT BEHAVIORS PROVED TO BE OF A RELATIVELY MILD DEGREE, AND THREE OF THE NONDELINQUENT PARTNERS WERE NOTED TO BE POTENTIAL DELINQUENTS, WITH DISCORDANCE BEING ONLY A MATTER OF EXTERNAL APPEARANCE. HOWEVER, UNEQUIVOCAL DISCORDANCE EXISTED IN ONE PAIR DUE TO DIFFERENCES IN PSYCHOPHYSIOLOGICAL DEVELOPMENT AND PSYCHOLOGIC MILIEU. FACTORS ACCOUNTING FOR THE DISCORDANCE WERE ANALYZED IN TERMS OF BIOLOGICAL MILIEU, INTELLIGENCE, PERSONALITY, AND THE PSYCHOLOGICAL ENVIRONMENT OF THE HOME DURING CHILDHOOD. IT WAS CONCLUDED THAT THESE FACTORS INTERACT IN A COMPLICATED MANNER AND, FURTHER, THAT PERSONALITY MATURATION PLAYS A SUBSTANTIAL ROLE, RESULTING IN MUTUAL INTERACTION OF THE BIOLOGICAL, PSYCHOLOGICAL AND SOCIAL ENVIRONMENTS. TABULAR AND GRAPHIC DATA IN JAPANESE ARE INCLUDED. (KBL)