The clinical course of two cases of spotted fever rickettsiosis was described including data of laboratory examinations and treatment. In addition, the clinical, laboratory, and epidemiological features of 23 confirmed cases experienced from 1983 to 1986 in the Muroto area of Kochi Prefecture were analyzed. Infections occurred in individuals of all ages irrespective of sex. The illness appeared from April to October. The incubation period was 4 to 7 days, although the vector has not been detected. Symptoms and signs were as follows: all cases developed a fever reaching 40°C. An erythematous rash covered the trunk and extremities in all cases, and it became hemorrhagic when patients received treatment late after the onset. In some cases the rash appeared on the palms. An eschar was found in half of the cases. Regional lymphadenopathy was noticed in 2 cases but no generalized lymphadenopathy was detected. Other clinical symptoms were anorexia, headache, vomiting, arthralgia, chill, malaise, hypotension and stupor. The CRP test showed strongly positive results, but leukocyte counts were within the normal range. In differential leukocyte counts, neutrophils increased and lymphocytes decreasd in the acute pahse, and vice versa in the convalescent phase; in many cases eosinophils disappeared. Three fourth of the cases showed an elevation of the serum transaminase activities. Specific immunofluorescence test with Rickettsia montana of spotted fever group demonstrated a significant rise in IgG and IgM antibody titers in all cases. Within 1 to 7 days after the onset, patients were treated with tetracycline antibiotics, resulting in defervescence and recovery within 2 to 5 days.