THERE are several factors which are seldom stressed in general discussion of the treatment of thyroid disease, which appear of great importance when dealing with actual patients. The first (in importance) of these factors is correct diagnosis of toxic symptoms. Almost one-third of the patients reporting to our clinic prove to have no disease attributable to the thyroid gland. A small fraction of this group report because of suspected goiters that prove not to exist. The majority report because of symptoms which wrongly suggest thyroid toxicity. Diagnosis of thyroid toxicity is far from being on a satisfactory basis. From the point of view of the patients, diagnosis is a double problem. It is easy to overlook thyroid toxicity, and case histories show that many thyro-toxic patients are overlooked and wrongly diagnosed for long periods, often by physicians of the highest standing. A few have been treated, for example, for diabetes, pulmonary tuberculosis, nausea and vomiting of pregnancy, and even operated on for acute surgical abdominal conditions. But the great majority of overlooked cases have been suspected of a heart disease. Obscure thyroid toxicity can suggest all these and other diseases. Those of us who are treating thyroid disease are not so directly concerned, perhaps, in cases of toxicity overlooked as in the correct diagnosis of those already suspected and sent to us for treatment. Of the many patients diagnosed as having thyroid toxicity, but who do not have it, a very small fraction have a heart disease or pulmonary tuberculosis or chronic nephritis. The overwhelming majority have no disease whatsoever but are in what may be called, for want of a better term, a neurasthenic state. Differentiating thyroid toxicity from neurasthenic states is a constant problem in a thyroid clinic, and at the risk of being tedious I wish to emphasize it. Before the World War it is fair to say there was no general recognition of a neurasthenic state simulating thyroid toxicity (and heart disease) as an entity, even among physicians dealing with large numbers of thyroid patients. During the World War so many soldiers of all armies were disabled by breathlessness, easy fatigueability on exertion or excitement, tremor, rapid heart, and vasomotor disturbances that investigation was forced. When physicians fresh from civil practice for the first time saw these cases grouped together in large numbers in army hospitals, they invariably felt that the cases had thyroid toxicity. (X-ray therapy directed at the thyroid gland, among many other measures, was recommended.) Very careful study of their symptoms was made from all available angles. This, and prolonged observation, served to convince the physicians studying these cases that the thyroid was not concerned in this condition. The condition was variously named “effort syndrome,” “soldier's heart,” and “neurocirculatory asthenia.”