Higher levels of IgE-containing immune complexes (IC) have been reported in sera from patients with allergic diseases than in sera from controls. To evaluate the possibility of an IC-mediated mechanism in the pathogenesis of bronchial asthma, we measured circulating C3-containing IgE IC (C3-IgE IC) using anti-C3 ELISA from 20 house dust mite (HDM)-sensitive asthmatics, 20 non-atopic asthmatics, and 14 non-atopic controls. C3-IgE IC levels were significantly higher in HDM-sensitive asthmatics (mean ± S.D.: 12.2 ± 7.8 AU/ml) than in non-atopic asthmatics (6.5 ± 7.5 AU/ml) or controls (5.8 ± 4.4 AU/ml). C3-IgE IC levels were significantly correlated with HDM-specific IgE levels (r = 0.50, p<0.05), but not with total IgE levels (r = 0.36, p< 0.05) in HDM-sensitive atopic asthmatics. C3-IgE IC levels in sera did not significantly change during HDM-bronchoprovocation test in six HDM-sensitive asthmatics who showed positive reaction. Part of C3-IgE IC could be precipitated by protein G coupled beads. In conclusion, C3-IgE IC levels were elevated in sera from HDM-sensitive asthmatics; moreover IgG antibodies might be a component of C3-IgE IC. Our results suggest that an IgE IC-mediated mechanism could be involved in the pathogenesis of atopic asthma.