Numerous workers have experimented with thyroid treatment in mental disorder ever since this drug was first introduced into therapeutics. While some of them have reported success in a small proportion of their cases, others have remained quite unconvinced of its efficacy, except in mental disorder secondary to recognizable myxódema, and have attributed the changes observed to the known tendency of psychotic patients to periodic fluctuations or spontaneous recovery. Thyroid has been used in a variety of ways. Doses ranging from 1 gr. up to 70 gr. of the thyroideum siccum a day have been prescribed, and as a result it has been found that many schizophrenic patients have an abnormal tolerance for thyroid. For instance, Hoskins (1929) reported the administration of 48 gr. of thyroideum siccum a day for six months to a schizophrenic patient who showed apparent improvement and no toxic effects; but he has pointed out that not all schizophrenics can tolerate these enormous dosages without being intoxicated and made worse. It has, however, been the deliberate aim of some workers in the past to produce an intoxication, but this method has now largely been abandoned.