Workers in the field of public health can perform their function far better if they work with the insights and concepts of psychiatry. There is a two-way learning process between psychiatry and public health. The mental hygiene approach is an integral and inseparable part of the philosophy of public health practice. Psychiatry's contribution is, however, contingent on an acceptance of the philosophy and aims of public health, a willingness to work within its administrative and functional organization, and a recognition of those mental hygiene objectives of public health which have already been achieved. The people who are served by public health activities have the usual psychiatric problems and are therefore greatly in need of mental hygiene services.