THE STUDY FOCUSES ON THE 55 PROBATION CASES (OUT OF A TOTAL OF 1,526 CASES TERMINATED BETWEEN OCTOBER 1973 AND SEPTEMBER 1975) IN WHICH PROSECUTION FOR BREACH OF PROBATION ORDER TOOK PLACE. THE CHARACTERISTICS OF THE FAILED PROBATIONERS ARE COMPARED WITH THOSE OF OTHER PROBATIONERS. COMPARISONS ARE ALSO DRAWN AMONG PROBATION OFFICERS WITH REGARD TO THEIR USE OF FORMAL SANCTIONS FOR VIOLATIONS. IN GENERAL, THE FAILED PROBATIONERS WERE CHARACTERIZED BY INSTABILITY AND BY FREQUENT CHANGES IN EMPLOYMENT, ADDRESS, AND SUPERVISING OFFICER. MEASURES OF PERSONAL AND ENVIRONMENTAL STRESS SUGGEST THAT THE FAILED PROBATIONERS HAD A POOR PROGNOSIS FROM THE BEGINNING OF THEIR PROBATION. PROBATIONERS SUBJECTED TO BREACH ACTION WERE MOST LIKELY TO BE YOUNG MEN. THE HIGHEST RATE OF BREACH, HOWEVER, WAS AMONG YOUNG WOMEN UNDER AGE 21. FAILURE OF THE PROBATIONER TO MAINTAIN CONTACT WITH THE SUPERVISOR WAS THE MAIN REASON FOR WHICH LEGAL ACTION WAS TAKEN. IN GENERAL, UNWILLINGNESS TO COOPERATE IN SUPERVISION WAS EVIDENT AT AN EARLY STAGE. THE MATURITY OF OFFICERS WHO RESORTED TO FORMAL SANCTIONS FOR VIOLATIONS SOUGHT THE OPINION OF ANOTHER OFFICER BEFORE DOING SO. THE OFFICERS VIEWED THE POLICE AND COURTS AS COOPERATIVE IN THE PROCESSING OF VIOLATORS. OF ALL THE OFFICERS' RECOMMENDATIONS, 90 PERCENT WERE FOLLOWED BY THE COURT. IN MOST CASES, CONTINUANCE OF SUPERVISION WAS RECOMMENDED. THE COURTS WERE LEAST LIKELY TO AGREE WITH THE PROBATION OFFICER WHEN THE OFFICER RECOMMENDED A CUSTODIAL SENTENCE. THERE WAS CONSIDERABLE VARIATION AMONG PROBATION OFFICERS IN THEIR USE OF FORMAL SANCTIONS. OFFICERS WHO RESORTED TO BREACH PROCEEDINGS WERE MOST LIKELY TO BE MALE, MIDDLE-AGED, AND EXPERIENCED IN PROBATION WORK. FURTHER STUDIES OF THE TASKS INVOLVED IN PROBATION WORK AND OF THE EXERCISE OF DISCRETION BY PROBATION OFFICERS ARE RECOMMENDED. SUPPORTING DATA AND A LIST OF REFERENCES ARE INCLUDED. (LKM)