Serum samples obtained from 55 patients with confirmed asthma induced by house dust mites, and 30 control subjects with no mite allergy, were investigated for specific IgG antibodies against the mites Dermatophagoides pt. and far. In 23 of the 55 asthmatics, specific hyposensitization treatment had previously been performed. Patients with allergic mite-induced asthma proved to have significantly higher specific IgG antibody titres than the control subjects. The difference between the groups with and without prior desensitization was not significant. All subjects with no IgE-mediated allergy vis-a-vis house dust mites (controls) had detectable specific IgG antibodies against both mites.