Abstract. IgG subclasses differ not only in their biochemical and biologic properties, but also in their occurrence as selective deficiencies, alone and in combination. The normal range of IgG subclass concentrations in children and adults is compared with deficiencies found in individuals with repeated respiratory tract infections. Concomitant IgA deficiency is often noted. It is suggested that decreased IgG2 and IgG3 levels in IgA‐deficient individuals may increase the risk of recurrent respiratory infection and lung damage. Finally, the efficacy of immunoglobulin prophylaxis in reducing incidence of infection is anecdotally related.