This study is concerned with the effectiveness of ECT as an adjunct to the psychotherapeutic treatment of 200 patients. It is found that effectiveness depends both on diagnostic entity and psychopathologic state. Thus, affective disorders responded best to ECT; paranoid reactions and psychoneurotic reactions with depression responded well; and schizophrenic reactions poorly. Influencing these results, however, was the fact that depression associated with agitation, anxiety, fear, or sexual content yielded better results, and depression associated with hostility, guilt, or body concern yielded poor results, in each diagnostic category. In the absence of depression, fear and sexual content yielded good results, and hostility, anxiety, and fixation yielded poor results. Optimal efficiency was obtained only when ECT was indicated by both diagnosis and psychopathologic state.It seems essential that information about differential effectiveness be determined for each of the physical treatments available in psychiatry. Only thus will it be possible to achieve maximum effectiveness and complementary utilization of these treatments.