It is suggested that the regulations of interlukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) genes expression are mediated through common pathway. To understand signal pathway of lymphokine gene expression, we screened IL-2, IL-3, IL-4, and GM-CSF gene expression in activated mouse mast cell, PB-3c. In PB-3c cells activated by PMA and A23187, lymphokine (IL-2, IL-3, IL-4, and GM-CSF) gene expressions were detected from 15 min. Cycloheximide did not affect expressions of the gene in activated PB-3c cells. IL-2 gene expression was induced in TPA / A23187 activated PB-3c cells only, but IL-4 gene expression was induced in A23187-activated PB-3c cells. IL-3 and GM-CSF gene expressions were induced in A23187-activated PB-3c cells, and the inductions of these gene were increased about 2.5 fold in TPA/A23187-activated PB-3c cells. In the pretreatment of protein phosphatase (PP) inhibitors, okadaic acid (PP2A and PP1 inhibitor) did not block the induction of the gene expreession. But in the pretreatment of cyclosporin A (PP2B inhibitor), inductions of IL-2 and IL-4 gene expressions were blocked completely, but IL-3 and GM-CSF gene expressions were decreased to about 20%. In the pretreatment of protein (ser/thr) kinase inhibitor, IL-2 and GM-CSF gene expressions were blocked completely, but IL-3 and IL-4 gene expressions were not affected. These results indicate that the induction of lymphokine gene expressions in activated PB-3c cells are mediated by different signal mediators. Moreover, PB-3c cells will provide a useful system to investigate the signal transduction pathway for induction of lymphokine gene expression.