• Rocky Mountain spotted fever was diagnosed in 74 patients at the University of Virginia Hospital from 1945 through 1954. During the same 10-year period the total number of cases reported in Virginia was 744 and the total for the United States was 4,517. Four case histories are given to illustrate the course of the disease, the history of exposure to tick bites, the recovery of youthful patients without specific treatment, and the fatal outcome in an older patient despite treatment. Persistent fever and a cutaneous eruption were the earliest dependable clinical findings suggesting the diagnosis. Among diagnostic tests, the Proteus-agglutination reaction is the most widely used, and the results were almost always positive by the 10th to 15th day of the disease. Treatment should be undertaken promptly without waiting for final diagnosis. The advent of the antibiotics, particularly chlortetracycline hydrochloride, oxytetracycline, and chloramphenicol, has greatly improved the prognosis.