The present experiment was a comparative test of two prominent models of phobia treatment: the exposure model, which emphasizes the extinction of phobic responses through prolonged exposure to feared stimuli, and the self-efficacy model, which emphasizes building a strong sense of mastery by promoting rapid performance accomplishments. Severe height and driving phobics were randomly assigned to one of three treatment conditions: (a) mastery-oriented treatment based on selfefficacy theory, (b) exposure treatment, and (c) no treatment. Although the two treatments were equivalent in duration of exposure and in the degree of inducement to confront threats rapidly, mastery treatment proved to be significantly more effective than exposure in restoring subjects' behavioral functioning, strengthening their perceived self-efficacy, and diminishing their anticipated anxiety and performance-related anxiety. Both treatments were more effective than the control condition. The results supported the hypothesis that treatments effect behavioral change through their intervening influence on perceived self-efficacy: Self-efficacy predicted therapeutic behavior change significantly better than did anxiety, exposure duration, or performance level achieved during treatment.