To the Editor: The results of Rodey and his colleagues1 confirm that the HLA antigens Dw3 and Dw4 are increased in black juvenile diabetics2 as they are in whites. Juvenile diabetes is rare in blacks in western Africa, where 99 per cent of American black slaves originated. However, 20 to 30 per cent of the gene pool of the American black population is composed of genes from whites. Since the frequency of juvenile diabetes in American blacks falls between that of African blacks and American whites, susceptibility to the disorder in American blacks can be explained by their having inherited. © 1980, Massachusetts Medical Society. All rights reserved.