The present study was undertaken to assess the importance of Chironomidae as an allergen causing bronchial asthma in Japan, and to evaluate histamine release as an allergy test in chironomid-midge allergic patients. Extracts of Chironomidae (T. akamusi and C. Yoshimatsui) caused the release of histamine in six out of 13 allergic patients with positive skin tests. In contrast, histamine release induced by these allergens was not observed in leukocytes from two asthmatic patients and five control subjects without IgE antibody as evidenced by negative skin tests and RAST. There was a significant correlation between maximal histamine release and IgE antibody levels. Furthermore, a significant inverse relationship between the concentration of allergen causing 25% histamine release (HR25) and IgE antibody levels was observed. The correlation coefficients, however, between histamine release and RAST were not high, and there were discrepancies between the two tests in some cases. These results suggest that Chironomidae induce histamine release from leukocytes via IgE-mediated mechanism but histamine release cannot be replaced by RAST and also suggest that chironomid midge is one of the important allergens in Japan.