We report the case of a 38-year-old woman who had pulmonary actinomycosis that involved the pleura and the pectoral muscles. The patient was initially treated with intravenous ceftriaxone once a day on an outpatient basis. After 3 weeks of treatment, a computed tomogram showed resolution of the initial findings. This result suggests that ceftriaxone may be an effective and convenient therapeutic agent for the initial parenteral treatment of actinomycosis.