An unusually severe case of Rocky Mountain spotted fever that failed to develop a rash by the eighth day of fever in spite of the delay in beginning specific chloramphenicol therapy until that time is reported. Due to the absence of a rash the diagnosis was of necessity only presumptive when chloramphenicol therapy was begun. It was not definitely established until later, when the agglutination and complement fixation tests became positive. Chloramphenicol effected a recovery within 48 hours of its initiation. This is the first reported case of severe tick fever to survive eight days of symptoms without specific therapy and yet fail to develop a rash.