Mouse mast cells produce many kinds of cytokines in response to cross-linking of high affinity Fc epsilon receptor (Fc epsilon RI). Among these cytokines, granulocyte-macrophage CSF (GM-CSF) gene induction in mouse mast cells has been reported to be regulated at both the transcriptional level and the post-transcriptional level. We analyzed the mechanism of the transcriptional regulation of GM-CSF gene induction through Fc epsilon RI cross-linking stimulation in the mouse mast cell line MC/9. In MC/9, the GM-CSF gene was activated transcriptionally by Fc epsilon RI cross-linking stimulation. The 5' deletion analysis of GM-CSF gene promoter indicated that the 5' boundary of the responsive promoter region lay between positions -113 and -95. When the deletion was extended to positions -72 or -60, the stimulatory effect was significantly diminished. We then examined 3' deletion of pmGMCAT -113 from position -60. This analysis indicated that the 3' boundary lay between positions -84 and -72. No subfragments of the region spanning positions -113 to -72 could cover the full induction level. A site-directed mutagenesis experiment revealed that the sequence spanning positions -108 to -72 was needed for full activation. These data indicate that GM-CSF gene in mast cells is activated mainly through the sequence spanning positions -108 to -72.