Effective treatment involves therapists responding appropriately to their clients' varying requirements, including clients' predominant interpersonal styles. In 2 manualized time-limited treatments for depression, psychodynamic–interpersonal (PI) and cognitive–behavioral (CB) clients were assigned to 1 of 3 interpersonal style groups. Therapists, who were not told their clients' interpersonal style, nevertheless responded with systematically different interventions depending on clients' interpersonal style. Consistent with predictions, therapists tended to use more affective and relationship-oriented interventions with overinvolved clients, particularly in PI therapy. Therapists tended to use more cognitive treatment methods with underinvolved clients, particularly in CB therapy. Outcomes of the interpersonal style groups were approximately equivalent, consistent with a view that the differences in treatment implementation reflected appropriate responsiveness to clients' interpersonal styles.