An unsuspected finding in this study was the high frequency of blank antigens in the three groups studied. This might be explained by the presence of unknown antigens in these populations as has been the experience of many investigators when HLA studiqs are applied to isolated populations or by the limited number of antigens used in this study (6). The sera of multiparous women from these populations are currently being tested among the individuals showing HLA blanks in an attempt to further define the blanks.