The rickettsial diseases of man in Japan include Tsutsugamushi disease (scrub typhus), murine typhus, which occurs sporadically, and one of spotted fever group diseases, recognized as a new entity since 1984. Starting from 1976, there has been a remarkable resurgence in the number of reported cases of Tsutsugamushi disease in Japan after several years of virtual absence, and endemics are still continuing after reaching a prominent outbreak in 1984. Its yearly incidences from 1982 to 1986 were 538, 749, 971, 890 and 738, respectively. This resurgence is most likely related to an increase of vector mite colonies that carry Rickettsia tsutsugamushi. However, it cannot be explained as to how these foci of vector mites developed. The existence of spotted fever group disease had not been recognized until quite recently. This rickettsiosis was first identified in Tokushima and Kochi Prefectures in 1984. To date, the estimated total number of sero-positive cases is over 45 cases. The causative rickettsiae were isolated from the blood of 5 patients using cell culture methods and the identification of these rickettsiae is now being carried out.