MANY IMPORTANT changes can be ascribed to the chemotherapeutic drugs and antibiotics. Striking examples of these changes are found in the clinical picture of empyema, its incidence, pathogenesis, and treatment. In the short space of twelve years the frequency of empyema among admissions to the thoracic section of the New Haven Hospital has dropped from 16.7% to 2.4%, or approximately one-seventh of the earlier level. The increasing use of antibiotics in the treatment of pneumonia, even though frequently outside of a hospital and sometimes without radiological or bacteriologic control, has sharply decreased the incidence of pneumococcal and streptococcal empyema. In very young infants staphylococcal pneumonia and empyema have come into a position of relative prominence. At the Royal Edinburgh Hospital for Sick Children, according to Macaulay, the staphylococcal form has increased from 3% to all pneumonias in 1929 to 55% in 1952. Because more and more intrathoracic surgery is being