Advantage was taken of an opportunity to study the effects of penicillin on Erysipelothrix rhusiopathiae, the causative organism of swine erysipelas. Owing to the fact that swine cannot readily be infected with erysipelas by artificial methods, pigeons which are highly susceptible to the disease, were selected to serve as experimental animals. It was the purpose of these studies to ascertain whether or not the swine erysipelas bacillus is sensitive to the drug and incidentally to determine the possibility of finding application of penicillin in the treatment of swine