For many years one of us (L. U.) has been interested in securing an ideal preparation to dissolve the thick tenacious material that impedes the respiration of patients with bronchial asthma and other respiratory conditions. In 1937, in collaboration with Albert H. Andrews, assistant clinical professor of bronchoesophagology at the University of Illinois Medical School, an aerosol was made of an enzyme derived from the fruit of the plant Carica papaya and was tested in animals and on 10 patients. The investigation, which was unpublished, was discontinued because of severe local reactions including bleeding and marked hoarseness. Recently, our interests were drawn to trypsin, a natural body enzyme that digests necrotic tissue without producing adverse action on living tissue. The effects of this enzyme on 73 patients are herewith reported. PHARMACOLOGY The highly purified crystalline trypsin used in this study and available as Tryptar is derived from mammalian pancreas and