IN COMPARING THE VARIETY OF INDICATORS OF SUCCESSFUL TREATMENT USED IN EVALUATING DRUG ABUSE TREATMENT PROGRAMS, IT IS CONCLUDED THAT THERE ARE FEW USEFUL INDICATORS DUE TO THE DIFFICULTY IN LOCATING AND INTERVIEWING EX-CLIENTS, THE DIFFICULTY IN OBTAINING DATA ON APPROPRIATE PRETREATMENT FACTORS, AND THE DIFFICULTY IN CONSTRUCTING CONTROL OR COMPARISON GROUPS. THE DISADVANTAGES TO USING RETENTION IN TREATMENT, EMPLOYMENT, SOCIAL FUNCTIONING, AND DRUG USE AS MEASURES OF TREATMENT OUTCOME ARE DISCUSSED. THE BASIC DISADVANTAGE OF EACH OF THESE MEASURES IS ITS INDICATION OF A SUBJECT'S CONDITION AT A GIVEN POINT IN TIME RATHER THAN OVER A PERIOD OF TIME, THUS MAKING IT DIFFICULT TO COMPARE PRETREATMENT AND POSTTREATMENT FUNCTIONING AND DEAL WITH FLUCTUATING BEHAVIOR OVER TIME. THE DISADVANTAGES OF USING ARREST DATA AS A MEASURE OF TREATMENT SUCCESS ARE IDENTIFIED AS FOLLOWS: (1) THE FULL RANGE OF INTENDED TREATMENT OUTCOMES ARE NOT DESCRIBED, (2) CRIMINAL BEHAVIOR IS NOT SHOWN PRECISELY; (3) LIKELIHOOD OF ARREST VARIES FROM ONE JURISDICTION TO ANOTHER; AND (4) SELF-REPORT ARREST DATA ARE NOT NECESSARILY VALID. THE PRINCIPAL ADVANTAGE OF ARREST DATA AS A TREATMENT OUTCOME MEASURE IS THAT THEY PRESENT A COMPREHENSIVE RECORD IN LINEAR FORM OVER A PERIOD OF TIME, THUS ALLOWING PRETREATMENT AND POSTTREATMENT COMPARISONS. ALSO, THE USE OF CENTRALIZED ARREST DATA INCREASES THE POSSIBILITY OF INCLUDING COMPARISON GROUPS IN A STUDY. RESULTS OF A NEW JERSEY EVALUATION WHICH EXAMINED 30 CLIENTS EACH IN 9 METHADONE TREATMENT PROGRAMS, IN 6 RESIDENTIAL PROGRAMS, AND 2 NONRESIDENTIAL DRUG-FREE TREATMENT PROGRAMS ARE REPORTED. EX-CLIENTS WERE FOLLOWED FOR APPROXIMATELY 17 MONTHS. ANALYSIS SHOWED THAT DATA ON ARRESTS CORRELATED SIGNIFICANTLY WITH EMPLOYMENT, DRUG USE, AND THE SUBJECT'S DEGREE OF SELF-REPORTED CONTENTMENT. REFERENCES ARE PROVIDED. (RCB)