The characteristics of laboratory data of Kudaka islanders in Okinawa prefecture were reported. The outstanding characteristic was a surprisingly high percentage in abnormal blood urea nitrogen (BUN). This was as high as 45.6% in Kudaka Jima as contrasted to only 2.3% abnormal in Naha area in Okinawa main land. This was not the result of many elder people living in this island. The percentage of abnormal BUN in a city in the southern part of Okinawa main land was 23.4%, about half of Kudaka

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... , even though only the people of more than 65 years old were examined. Moreover, in any decade, even in the 30th decade, the percent abnormality in Kudaka Jima was higher than that of 65 years old or elder people in Itoman city. The reason for this high percentage in abnormal BUN was not clear at this time, but possible effects of latent kidney malfunction, quality of the water, and hereditary factor of Kudaka islanders were discussed.