The social worker at the Boston Dispensary works actually in the clinic. Here she meets each new patient and takes a careful social history, usually before the patient sees the physician. Often she is present when the doctor interviews the patient, and always, after this interview, the physician consults with the social worker. Then a plan of treatment is made which includes the social as well as the medical factors of the case. In a certain proportion of cases, home visits are not necessary. The efforts of the social worker in the clinic itself are sufficient to secure adequate treatment. Thus there appears a very important classification of the kinds of social work required: 1. Patients presenting acute family problems of poverty, ignorance, or undesirable home conditions and associations. These patients require home visits and intensive social work. In the mental clinic of the dispensary they constituted 48 per cent of the 141 patients. 2. Patients requiring a home visit simply for the purpose of insuring the patient's return to the clinic--that is, cases in which there were no complex home problems but in which it was necessary to go to the home once in order to persuade the patient to come back for treatment. This class at the Dispensary constituted 20 per cent. 3. Patients to whom it was possible to give effective treatment by clinical interviews only, without home visits. This class constituted 32 per cent. Inasmuch as the cost of the service per patient (estimating the time taken by the social worker) is enormously greater in class one than it is in class three, it is highly important to make this classification, and to keep a close watch upon the proportion of the different types, so that the cost of the work as a whole, with reference to its efficiency, can be accurately estimated. An efficiency study from this standpoint during 1912 leads to the conclusion that the average cost per patient (the complete treatment of a case) in class three is sixty cents; in class two, a dollar; in class one, four dollars. The medical service is given gratuitously by the physician. More extended studies in this and in other mental clinics should be made in order to work out the cost figures more accurately. There can be no doubt, however, that even if the cost of medical service were added, it is cheaper to treat mental diseases in the early stages, when patients can retain their places in the community, wholly or partly self-supporting, than to let the disease reach a point where permanent damage is done, and the insane hospital is the only resource.