The new antibiotic aureomycin has been found to possess a favorable chemotherapeutic effect against Hemophilus influenzae. Recently its protective ability against experimental infection by this organism has been demonstrated.1In vitro studies have shown aureomycin to lie inhibitory in concentrations varying from 0.9 to 5.0 micrograms per cubic centimeter of medium.2 Aureomycin is a yellow, crystalline antibiotic substance obtained from Streptomyces aureofaciens. Its therapeutic effectiveness in diseases caused by numerous gram-negative organisms and by the rickettsiae and in certain viral-like infections is now a matter of record. It is soluble in both acid and alkaline solutions. Aureomycin, prepared as the hydrochloride, has apH of 2.5; whereas thepH of the sodium salt in carbonate buffer is 8.5. The drug is well tolerated both orally and intravenously. Acute toxicity is not seen in mice when 1,500 mg. per kilogram of body weight are administered orally, and