Serial determinations of serum levels of IgA, IgD, IgG, and IgM globulin were performed on 27 children with anaphylactoid purpura and two children with acute poststreptococcal glomerulonephritis. Ten of 20 children with anaphylactoid purpura seen within 3 months of the onset of the skin rash had significant elevations of their serum IgA globulin. The other immunoglobulin levels were normal in the remaining children and those with acute poststreptococcal glomerulonephritis. The selective elevation of serum IgA globulin may be related to the pathogenesis of anaphylactoid purpura.