69 Caucasian children, 34 with non-atopic and 35 with atopic bronchial asthma, demonstrated different, Gm-associated IgG antibody responsiveness. The non-atopic bronchial asthma group showed a preponderance of the Gm(a,'',g) haplotype, while the atopic study group showed a preponderance of the haplotype with the alternative allotypes on all IgG subclass loci, namely Gm(f,n,b). Patients with non-atopic bronchial asthma showed a significantly increased frequency of the phenotypes containing the Gm(a,'',g) haplotype, namely the Gm(a,'',g/a,'',g) and Gm(a,'',g/f,'',b), and an increased number of individuals were homozygous G2m('','') on the IgG2 locus. The 2 asthma groups showed different characteristic IgG subclass patterns, the non-atopic group with significantly decreased IgG2 and IgG3, especially those of the Gm(a,'',g/a,'',g) phenotype, and the atopic group with significantly increased IgG1 and IgG4, especially those of the Gm(f,n,b/f,n,b) phenotype. The characteristic IgG subclass patterns originate from the different Gm phenotypes found in the 2 groups. The results emphasize the presence of qualitatively and quantitatively different IgG molecules in non-atopic and atopic bronchial asthma patients and show the interest in studying IgG genes and IgG molecules as markers of pathogenesis. G2m('','') homozygosity is a new important marker of non-atopic bronchial asthma.