['IL-5 plays a central role in allergic diseases associated with eosinophilic inflammation. We have previously reported that IL-5 production by peripheral blood mononuclear cells (PBMC) is greatly enhanced in both atopic and nonatopic asthmatics compared to control subjects.', 'Concanavalin A (Con A) blast lymphocytes were derived from PBMC of allergic and control subjects. Transcriptional regulation of the IL-5 gene was investigated by transient transfection assay.', 'A significant amount of IL-5 was produced by Con A blast lymphocytes derived from allergic subjects upon stimulation with phorbol ester and Ca(2+) ionophore, whereas the cells derived from control subjects did not produce a detectable amount of IL-5. Production of IL-2 and IL-4 was not significantly different between the two groups. A luciferase reporter plasmid containing the human IL-5 promoter/enhancer region was transcribed by Con A blast lymphocytes derived from allergic subjects, but not by the cells from control subjects, upon activation.'] Is iL-5 synthesis by T cells of allergic subjects regulated at the transcriptional level?