A method is presented for adm. penicillin dust by inhalation. Of the 66 subjects used in the expt., 55 had upper respiratory tract infections, and 9 had lower respiratory tract infections. All patients received 100,000 U. of penicillin dust by inhalation for 20 min. 3X a day. The bronchiectatic patients revealed less cough and secretion on dismissal. The patients with chronic bronchitis showed a moderate improvement. The symptoms of > 70% of those patients with acute conditions of the respiratory tract cleared up markedly, in many instances after only 1-2 treatments. Patients with diseases of the lower respiratory tract were given 10-16 treatments in from 4-6 days. No sensitivity reactions to penicillin occurred. Blood levels ranged from .03-1.92 U./ml. and indicated slow absorption, the max. level being obtained 2 1/2-3 1/2 hrs. after the inhalation. This new method appears more effective than other aerosol methods in ridding the upper respiratory tract of Gram-positive bacteria. The protracted effective absorption offered by this method suggests possible use of inhalation treatment for systemic conditions other than those of the respiratory tract.