THIS ARTICLE DEALS WITH RESEARCH ON EFFECTIVE TREATMENT METHODS FOR CONVICTS UNDER 26 WITH ADVANCED CRIMINAL TENDENCIES. SUCH CONVICTS ARE LISTED AS TYPE YB--AN INTERSECTION OF THE CLASS OF OFFENDERS UNDER 26 (Y) AND THE CLASS OF CONVICTS WITH ADVANCED CRIMINAL TENDENCIES (B). THROUGH THE USE OF THE MJPI PERSONALITY INDICATOR TEST, THE CHARACTERISTICS OF 503 MEMBERS OF THE YB CLASS WERE COMPARED WITH 552 OFFENDERS UNDER 26 WITHOUT ADVANCED CRIMINAL TENDENCIES, CLASSED AS YA, AND 520 MEMBERS OF CLASS B TYPE WHO WERE OVER 26. THOSE SUBJECTS SELECTED FOR STUDY WERE AT INSTITUTIONS IN VARIOUS LOCATIONS ALL OVER JAPAN. SUBJECTS WERE ANALYZED BOTH IN TERMS OF IQ AND PSYCHOLOGICAL STABILITY, AS WELL AS SOCIAL INTERACTION, FAMILY SITUATION, RECORD OF GANG MEMBERSHIP, AGE AT WHICH OBSERVED CRIMINAL BEHAVIOR BEGAN, AND PREVIOUS CRIMINAL RECORD. SURVEYS WERE MADE ALSO AS TO THE EXPRESSED NEEDS, HOPES, GOALS, AND OPINIONS OF THE SUBJECTS, TO DETERMINE THEIR SENSE OF VALUES. FINDINGS INCLUDED THE FOLLOWING POINTS: (1) THERE WERE NO SIGNIFICANT DISTINCTIONS IN INTELLIGENCE OR TEMPERAMENT FOR MEMBERS OF THE YB GROUP AND SO NO SPIECAL RECOMMENDATIONS FOR TREATMENT COULD BE MADE ON SUCH BASES; (2) YB OFFENDERS DID NOT HAVE DISTINCTIVELY BAD FAMILY BACKGROUNDS BUT DID TEND TO BELONG TO GANGS (THIS TENDENCY COULD BE USED CONSTRUCTIVELY BY ENCOURAGING THEM TO BECOME INVOLVED IN EDUCATIONAL AND RECREATIONAL GROUP ACITVITIES); (3) THOSE WITH MORE CONFIRMED CRIMINAL BEHAVIOR SHOULD BE TREATED SEPARATELY; (4) BETTER WAYS MUST BE FOUND TO ENCOURAGE YB SUBJECTS TO PARTICIPATE IN TREATMENT PROGRAMS. NUMEROUS STATISTICAL TABLES AND GRAPHS ACCOMPANY THE TEXT. --IN JAPANESE.