The release of histamine from basophils induced by anti-lgE and calcium ionophore A 23187 ( Cal) was examined in 27 patients with bronchial asthma and 7 healthy subjects, using a whole blood method. (1)The release of histamine induced by anti-IgE and CaI was significantly higher in atopic asthmatics than in non-atopic cases. (2) The histamine release with anti-lgE and CaI was significantly lower in cases with long-term steroid therapy compared to the release in cases without steroid therapy. (3) The release with anti-lgE and CaI was increased in cases with age of 0-39 years and in cases wpth age at onset of 0-39 years. (4) Anti-IgE induced release correlated to a certain extent with the release induced by CaI. These results show that basophil reactivity as expressed by histamine release changes under different conditions.