Abstract: Heat-killed, terminally sterilized saline suspensions of Propionibacterium acnes, Propionibacterium avidum, Propionibacterium lymphophilum, Propionibacterium granulosum, Cornynebacterium parvum, and Arachnia propionica are effective in treating viral infections of the respiratory tract in humans, and to induce the regression of dermal tumors and warts in humans. The potency of a saline suspension of heat-killed, terminally sterilized saline suspension of Propionibacterium acnes (P. acnes) was demonstrated through a laboratory animal challenge model. The P. acnes product is administered orally for the purpose of preventing or treating viral infections of the respiratory tract in man. The P. acnes preparation is intralesionally administered into dermal tumors, warts such as plantar warts, or other warts in people caused by the human papilloma virus, to cause regression of such dermal tumors and warts. The subcutaneous route of administration of the P.