In 50 consecutive atopic Caucasian patients with increased IgE > 600 kU/l, the phenotypic Gm allotype constellation deviated from that to be expected, with significantly increased frequency of patients with the phenotype Gm(fnb). There was an increased frequency of the G2m(n) allotype, more frequent in patients with IgE > 1,000 kU/l, and in patients with IgG4 > 1 g/l. In patients with IgE > 1,000 kU/l, the phenotype Gm(afnb) was significantly increased and in patients with IgG4 > 1 g/l the phenotype Gm(fnb) was significantly increased. Those atopic patients with increased IgE and increased IgG4, according to earlier studies known to have the most severe forms of the disease, were thus mainly found to have the m(fnb) phenotype.