Among children and young adults, both in the Black and the White populations of Virginia, serum immuno globulin A (IgA) concentrations were significantly lower in non secretors than in secretors. Whites showed the same pattern for IgG concentrations, but no trend was observed for IgG in Blacks nor for IgM or IgD in either Blacks or Whites. The effect of secretor status on IgA concentrations appears to be large enough to be of biological importance in streptococcal throat infections and, perhaps can explain the well documented effect of secretor status on the incidence of rheumatic fever and rheumatic heart disease – diseases occurring more frequently in non-secretors than in secretors.