The authors briefly describe biofeedback techniques such as EMG feedback, temperature feedback, and heart rate feedback, along with reports from the literature about their application to specific problems such as subvocalization while reading, Raynaud's disease, cardiac arrhythmias, and epilepsy. Many clinical applications of biofeedback are aimed at inducing relaxation, a state that has important psychotherapeutic potential. The authors suggest that biofeedback could be used to reduce a patient's general level of arousal or as an adjunct to behavior therapy or insight therapy. While there have been no reports in the literature of any harmful effects secondary to feedback training, the authors caution that some patients may respond negatively to an objectively measured state of relaxation.