PURPOSE: The expression pattern of c-jun by ionizing radiation according to cell growth state (exponential growth phase vs. stationary phase) and its relationship with cell cycle redistribution were investigated. MATERIALS AND METHODS: The exponential growth phase (day 4) and stationary phase (day 9) cells were determined from cell growth curve according to the elapse of days in CaSki. The cells were irradiated using 6 MV X-ray with a dose of 2 Gy at a fixed dose rate of 3 Gy/min. Northern blot analysis was performed with total cellular RNA and cell cycle distribution was analyzed using flow cytometry according to time-course after irradiation. RESULTS: The maximum expression of c-jun occurred 1 hour after irradiation in both exponential growth and stationary phase cells. After then c-jun expression was elevated upto 6 hours in exponential growth phase cells, but the level decreased in stationary phase cells. Movements of cells from G0-G1 to S, G2-M phase after irradiation were higher in exponential growth phase than stationary phase. CONCLUSION: c-jun may be involved in the regulation of cellular proliferation according to the growth states after irradiation.