The tissue types, immunoglobulin levels, and the presence of circulating autoantibodies were investigated in 57 children. Fifteen of these children suffered from bronchial asthma and, in addition, had no or very little IgA in their serum and saliva (Group 1 patients). Another fifteen children with asthma but normal immunoglobulin levels in serum and saliva (Group 2 patients), seven patients with selective IgA deficiency but without allergic diseases (Group 3 patients), and twenty healthy children served as controls. Sixty per cent of the Group 1 patients had the phenotype HLA-A1,B8, whereas this tissue type was found only in 27, 14 and 15 per cent, respectively, of the Group 2 and Group 3 patients and the healthy children. Furthermore, high IgM- and IgE levels were observed in most Group 1 patients, and in five of these patients (33 per cent) autoantibodies were present in the serum. In addition, eczema and glomerulonephritis occurred rather frequently in this group of patients. Conversely, normal immunoglobulin levels and absence of circulating autoantibodies were found in the remaining three groups of children. The results emphasize the heterogeneity of the IgA deficiency syndrome, and the question is raised as to whether the tissue type HLA-A1,B8 observed in most Group 1 patients reflects the abnormal immune reactivity of these patients.