Systematic desensitization is indicated for phobias, obsessions, compulsions, and anxiety reactions that are maintained by anxiety-reducing defense mechanisms. The technique involves instruction in deep muscle relaxation, construction of an anxiety hierarchy, and stepwise pairing of relaxation with imagined anxiety-provoking scenes. The basic principle is that relaxation is incompatible with anxiety. Relaxation can be induced by direct instruction, drugs, carbon dioxide, hypnosis, positive imagery, and a metronome-conditioned method. More than 100 outcome studies indicate that systematic desensitization produces significantly better results than a variety of comparison therapies.