Serum concentrations of specific IgE and IgG4 to dog and cat dander in subjects with allergy to both dog and cat were all higher than those in subjects without allergy to dog or cat (dog-specific IgE, 2.49 vs 0.26 kUA/L, P < 0.001; cat-specific IgE, 5.00 vs 0.62 kUA/L, P < 0.001; dog-specific IgG4, 1.75 vs 0.85 kUA/L, P < 0.01; cat-specific IgG4, 0.50 vs 0.30 kUA/L, P < 0.05). This evidence concerns the gene IGHE and allergic disease.