BACKGROUND: Helper T cells and T cell cytokines play central roles in allergic disorders including bronchial asthma. We reported enhanced IL-5 production by peripheral blood T cells of asthmatic patients. A transcription factor, GATA-3, has been implicated in IL-5 gene expression. This study was undertaken to clarify the role of GATA-3 in the upregulation of IL-5 synthesis in asthmatic patients. METHOD: Peripheral CD4+ T cells were transfected with an IL-5 promoter reporter construct as well as its mutants in the presence or absence of a GATA-3 expression vector. Messenger RNA expression level of GATA-3 in CD4+ T cells of asthmatic subjects was compared to that of healthy donors. RESULTS: IL-5 promoter activity in CD4+ T cells was enhanced by overexpression of GATA-3, whereas it was diminished by the introduction of mutations in the putative GATA-3 binding sites. The GATA-3 expression level in CD4+ T cells of asthmatic patients was equivalent to that of healthy controls. CONCLUSION: The expression level of GATA-3 may not be an essential factor to cause IL-5 hyperproduction in bronchial asthma, though GATA-3 is crucially involved in IL-5 gene transcription in human peripheral CD4+ T cells.