In Aioi, a village in the eastern part of Kagawaken near the border of Tokushima, an eruptive febrile disease with glandular swelling developed in summer. The death rate is found to be comparatively high. 1 made the study on the so called "Umayado Disease" broken out in Aioi-mura in summer to Mr. Mitani and Mr. Tanizawa of Tsuda-cho, a town about 15km northwest of Aioi in winter. From each of the patients, a Rickettsial strain is isolated by intraperitoneal transmission through the mice. I have performed serological tests about the Rickettsia isolated. I have discovered that these Rickettsia strains are nothing but Rickettsia tsutsugamushi. The data examined are as follows. 1. By intraperitoneal transmission, Rickettsial strains isolated have high virulence against mice. I can have succesive transmission easily and LD50 of brains, liver and spleen are 6.1, 6.9, and 7.1 respectively in Tanizawa strain, 6.3, 7.1, 7.3 respectively in Mitani strain. Again, the transmission of strains isolated by intranasal infection is possible. 2. The inoculation test into rats shows that the exudation of the abdominal fluid is scare, the Rickettsia is rarely proved by smearing and Maxcy's phenomenon is not observed. Transmission by intranasal inoculation is possible and we can see consolidated lung about 10 days after inoculation, and impression smears stained with Giemsa's stain revealed Rickettsia. 3. The inoculation test into guinea pig shows that Rickettsia appears in its peritoneal cavity by intraperitoneal inoculation but the Neill-Mooser's Reaction is not seen usually. 4. The intratestinal inoculation into rabbits causes its testinal swelling frequently. and can have successive transmission of strain by the testinal route. The intraocular inoculation test give rise to the acute iritis and the typical Rickettsia appears in the cells of Descement membrane. 5. The guinea pig, mouse. and rabbit inoculated with the isolatod Rickettsia strains produce antibodies which agglutinate OXK only. 6. The complement fixation test between the antisera of the isolated strains and R. prowazeki or R. mooseri is negative usually. So we can recognize that Rickettsia isolated by me is different from R. prowazeki or R. mooseri. 7. The intra or subcutaneously inoculated monkey with the Mitani strain produce ulcer on the inoculated place, and glandular swelling, with critical condition. Serum from the monkey 21 days after inoculation shows the positive agglutination titer of 1:1280 against OXK. By reinoculation with Tanizawa strains, the monkey develops some slight symptoms 14days after reinoculation. 8. The strains isolated by me did not increase at thioglycolate-broth, blood-agar, and glucose-broth during 7 days after inoculation. 9. Concerning the neutralization test between the strains isolatd and the other standard strains, I can say as follows. The Mitani strain showed that it belongs nearer to the Ozeki strain than to the Shichito strain or Karp strain. On the contrary the Tanizawa strain to Shichito strain rather than to the Ozeki strain or Mitani strain. Consequently, it became clear that the "Umayado Disease" of which the one type breaks out in summer in Aioi-mura and the other in winter in Tsuda-cho is nothing but the Tsutsugamushi disease. These two types differ only in antigenic structure of Rickettsia isolated from patients. It means that in Kagawaken we have two kinds of Rickettsia tsutsugamushi strains that differ in developing places and time and etiological nature.