The material studied consisted of tissue cells in primary culture from a variety of organs obtained from 218 legally aborted fetuses, ages 1 to 7 months. Regardless of sex, age, tissue, organ or experimental method the vast majority of cells showed a consistent value of 2x =46 chromosomes. The incidence of polyploidy and of abnormal cells was small. Except for the morphological difference in the sex chromosomes of the 2 sexes, the chromosomes were identical in all specimens studied. Likewise, there was no difference among the X or Y chromosomes from different organs of the same individual, or from different individuals. There is thus no evidence of chromosome polymorphism in the Japanese population. The karyotype for the Japanese people does not differ significantly from that established for American and European whites.