In fifty three mongrel dogs transferred from the Okinawa animal control center to our laboratory, Babesia organisms were tempted out for detection by splenectomy and dexamethazone administration. As a result, 11 strains of Babesia organisms were detected in 10 dogs, 7 strains were large and resembled B. canis, and 4 were small resembling B. gibsoni. The blood drawn from the dog most heavily infected with the large parasites was inoculated into 3 healthy mongrel dogs, and the heaviest parasitemia drawn from these three dogs was prepared in liquid nitrogen. This prepared blood was inoculated into a beagle designated C-11. In turn its blood, once confirmed to be infected, was inoculated into beagle C-12. Infected blood drawn from C-12 was passaged to a third beagle designated as C-13. C-12 was subsequently inoculated with B. gibsoni after the large parasites had disappeared from its peripheral blood. Serial examinations were continued until the dog's death. IFA testing was done on the sera of the inoculated beagles both prior to inoculation, and after the appearance of parasites in the peripheral blood. Sera from C-11 and blood smears containing large parasites were sent to Dr. Ristic, for identification. From data obtained in this research, and Dr. Ristic's independent results, the large parasites detected by us from dogs on Okinawa Island were concluded to B. canis.