HLA-A, B, C typing was performed on 37 unrelated healthy blood donors with selective deficiency (less than 0.05 g/l) or total lack (less than 0.00002 g/l) of serum IgA. A significant increase in HLA-B8 and A1 antigen frequency was found in the 15 individuals with lack of serum IgA. This was not observed among those 22, who had only deficiency of serum IgA (0.00002-0.05 g/l). The HLA antigen frequencies were compared to those of 900 randomly selected healthy blood donors. Increased frequency of HLA-A1 and B8 in association with total lack of serum IgA, but not with deficiency has not been demonstrated before. On the basis of this result it seems conceivable that lack of serum IgA may be caused by a different, perhaps genetically determined, mechanism than IgA deficiency.