Basophil histamine release induced by allergens (house dust and Candida albicans) and anti-IgE was examined in 31 patients with bronchial asthma in relation to patient age, age at onset of the disease and serum IgE levels. Basophils from patients under 40 years of age generally released a significantly large amount of histamine by stimulation with house dust and anti-IgE. On the other hand, histamine release from patients over 41 years of age was generally not marked when the cells were incubated with house dust and anti-IgE, although, in some cases, the release induced by C. albicans was fairly marked. Basophils from patients under 30 years of age at onset were reactive to house dust and anti-IgE, while the cells from patients over 41 years of age at onset tended to be reactive only to C. albicans. Basophils from patients with low serum IgE levels were less reactive than the cells from patients with high levels of IgE to house dust and anti-IgE. C. albicans-induced release of histamine did not correlate with serum IgE levels.