THE STUDY SUBJECTS WERE 1,575 MALE PRISONERS SENTENCED TO IMPRISONMENT WITH FORCED LABOR IN JAPAN. OF THESE, 503 WERE CLASS YB PRISONERS (YOUNG ADULTS UNDER AGE 26 WITH ADVANCED CRIMINAL TENDENCIES), 552 WERE CLASS YA PRISONERS (YOUNG ADULTS UNDER AGE 26 WITHOUT ADVANCED CRIMINAL TENDENCIES), AND 520 WERE CLASS B PRISONERS (PRISONERS WITH ADVANCED CRIMINAL TENDENCIES). THE SUBJECTS COMPLETED PERSONALITY, ATTITUDE, AND OTHER TESTS DESIGNED TO HIGHLIGHT FACTORS DIFFERENTIATING THE YB GROUP FROM THE OTHER GROUPS. FINDINGS ARE SUMMARIZED RELATIVE TO PERSONALITY TRAITS, FAMILY BACKGROUND, CRIMINAL BACKGROUND, ATTITUDE TOWARD IMPRISONMENT AND TREATMENT, ATTITUDE TOWARD OTHER INMATES AND PRISON STAFF, AND VALUES. CLASS YB PRISONERS WERE FOUND TO BE INTELLIGENT, LIKELY TO BE UNEMPLOYED AND LIKELY TO BELONG TO GANGSTER ORGANIZATIONS. MANY OF THE YB PRISONERS WERE HABITUAL PROPERTY OFFENDERS WHO HAD COMMITTED THEIR FIRST OFFENSE AT AN EARLY AGE. THE YB PRISONERS TENDED TO BE DEMANDING WITH REGARD TO THEIR DAILY NEEDS (FOOD, CLOTHING, ETC.), TO HAVE BLEAK OUTLOOKS, TO DISLIKE DISCIPLINE AND FORMALITIES, AND TO LACK A SENSE OF SOLIDARITY WITH FELLOW INMATES. YB PRISONERS ALSO EXPRESSED NEGATIVE ATTITUDES TOWARD THE PRISON AND PRISON STAFF. INMATES WITH ADVANCED CRIMINAL TENDENCIES ADAPTED TO PRISON LIFE MORE READILY AND APPEARED TO BE MORE STABLE ON THE SURFACE THAN DID INMATES WITHOUT ADVANCED CRIMINAL TENDENCIES. INMATES WITH PESSIMISTIC VIEWS OF THEIR FUTURES WERE LESS AMENABLE TO TREATMENT THAN WERE OTHER INMATES. RECOMMENDATIONS FOR IMPROVING TREATMENT FOR THE YB PRISONERS IN LIGHT OF THEIR CHARACTERISTICS AND ATTITUDES ARE OFFERED. NO TABULAR DATA ARE PROVIDED. (LKM)