THE EFFECT OF CLIENT VARIABLES, INTERVENTION TECHNIQUES, AND THE SERVICE DELIVERY SYSTEM HAVE OFTEN BEEN STUDIED AS FACTORS WHICH AFFECT THERAPY OUTCOME; HOWEVER, LITTLE HAS BEEN DONE TO DETERMINE THE EFFECT OF THERAPIST VARIABLES ON TREATMENT. SIMILARLY, LITTLE ATTENTION HAS BEEN GIVEN TO THE PROCESS THROUGH WHICH THE THERAPIST PERSUADES OR MOTIVATES PARENTS, TEACHERS, OR INSTITUTIONS TO APPLY TREATMENT PRINCIPLES. THIS STUDY WAS AN ATTEMPT TO INVESTIGATE THE PROCESS OF SYSTEMS-BEHAVIORAL INTERVENTIONS WITH DELINQUENT FAMILIES, BASED ON THE CONTENTION THAT WHILE THE PRINCIPLES OF BEHAVIOR CHANGE ARE REASONABLY WELL ESTABLISHED, THE PROCESSES THROUGH WHICH CLIENTS ACCEPT THESE PRINCIPLES ARE NOT. SEVERAL THERAPISTS WERE TRAINED IN BEHAVIOR MODIFICATION, AND WERE ASSIGNED DELINQUENT FAMILIES FROM THE UTAH REFERRAL AGENCIES. THERAPISTS WERE RATED ON THE FOLLOWING BEHAVIORS: AFFECT-BEHAVIOR INTERVENTION, WARMTH, HUMOR, BLAMING, SELF-DISCLOSURE, DIRECTIVENESS, SELF-CONFIDENCE, AND CLARITY. THESE VARIABLES WERE CORRELATED WITH OUTCOME MEASURES FOR TREATMENT OF THE DELINQUENT FAMILIES. THE DATA SUGGESTED THAT THERAPIST RELATIONSHIP SKILLS, HERETOFORE OVERLOOKED IN THE BEHAVIOR MODIFICATION LITERATURE, MAY BE CRUCIAL DETERMINANTS OF THERAPY SUCCESS. (AUTHOR ABSTRACT MODIFIED)