Empirical studies are reviewed, the aim being to investigate characteristics of the therapeutic relationship in cognitive-behavior therapy (CBT) and to identify therapist or patient interpersonal behavior that affects treatment outcome. CBT is characterized by a more active and directive stance on the part of the therapists and higher levels of emotional support than are found in insight-oriented psychotherapies. Therapists express high levels of empathy and unconditional positive regard, similar to those expressed by insight-oriented psychotherapists. Two clusters of interpersonal behavior have been identified that are clearly associated with CBT outcome: (a) the Rogerian therapist variables--empathy, nonpossessive warmth, positive regard, and genuineness; and (b) therapeutic alliance. There is some evidence for the impact on outcome of three additional clusters of patient behavior: (a) the patients' perception of the therapist as being self-confident, skillful, and active; (b) the patients' openness to discuss their problems; and (c) the patients' pretreatment predisposition to change and to accept psychological treatment as a means of achieving this. It is further concluded that relationship factors in general have a consistent but moderate impact on CBT outcome.