T^HIS paper reports the results of studies of the ABO, MN and Rh blood groups, 1 and of the haptoglobin, transferrin and acid phosphatase traits in the population of the Yap Islands, Micronesia. Blood samples were taken from 450 natives of these islands, with the results as shown in Table 1 below. With the exception of a study of the ABO blood group in 213 Yapese by Takasaki (quoted in Boyd, 1939), no previous extensive blood genetical studies have been carried out in these peoples. Hainline (1965) reported on hospital records for ABO and Rh(D) testing. Simmons et al. (1965) reported on only 17 individuals from the Yap Islands proper. Extensive anthropometrie studies were conducted in 1947-48 by E. E. Hunt, Jr. (1950Λ, 19506), and by Hainline in 1965-66. The field work on which this study was based was carried out by one of us (JH) during the period of June 1965 to September 1966.1 Laboratory analyses were performed at the Red Cross Blood Transfusion Service, Sydney, Australia.