To investigate the eosinophilia in patients with bronchial asthma (BA), we examined the release of eosinophil colony stimulating factor (Eo-CSF) from blood mononuclear cells (MNC) and lymphocytes from BA. We also investigated the effect of specific antigens on the release of Eo-CSF to determine its relation to other known Eo-CSFs. 1) Phytohaemagglutinin (PHA) and interleukin (IL)-2 at optimal concentrations stimulated mononuclear cells from BA, and induced Eo-CSF release. In contrast, MNC from normal volunteers released Eo-CSF with only PHA, but did not release Eo-CSF with IL-2. 2) Lymphocytes from BA who were sensitive to house dust mite and Dermatophagoides farinae (D. farinae) antigens responded to specific antigens with Eo-CSF production, but those from normal volunteers did not. 3) The anti-IL-3, anti-IL-5, and anti-granulocyte-macrophage (GM)-CSF antibody inhibited Eo-CSF activity in culture media of lymphocytes from BA. These results indicate that the increase in responsiveness of lymphocytes from BA to specific antigens and cytokines produced by T cells play an important role in the induction of eosinophilia in BA.