Effects of γ irradiation on mitogen-activated protein kinases （MAPKs） were examined in IEC-6 cells. In response to γ irradiation, Phosphorylation of intracellular signal-regulated protein kinase （ERK） was not significantly altered. The levels of phosphorylated forms of c-Jun NH,2,-terminal kinase （JNK） and p38 MAPK increased at 30 min following exposure to 6Gy γ irradiation, while the cell viability was lowered significantly at 12h. On the other hand,no clear changes were found in the total protein levels of ERK,JNK and p38 MAPK. Chelation of intracellular Ca,2+, suppressed γ irradiation induced JNK and p38 MAPK phosphorylation almost completely, but removal of external Ca,2+, did not. Activation of p38MAPK, but not ERK,was correlated with γ irradiation induced apoptosis. The present results showed that γ irradiation is a potent activator of JNK and p38 MAPK,and Ca,2+, mobilized from intracellular stores plays an important role for the activation of MAPKs and the induction of apoptosis in IEC-6 cells.