The effect of high pressure on proliferation and cell cycle progression was examined using murine erythroleukemia (MEL) cells. The MEL cells were exposed to high pressures (0.1-130 MPa) and then cultured for 5 days at atmospheric pressure. The proliferation of MEL cells was unaffected up to 60 MPa, but was suppressed at 80-110 MPa. Above 120 MPa, the cells were fragmented. The cell cycle analysis of 80 MPa-treated MEL cells showed that the cells in S phase are most sensitive to high pressure and they arrest in G2 phase. Interestingly, G2-arrested cells reinitiated DNA synthesis, resulting in giant cells with high DNA contents. Furthermore, when such G2-arrested cells were exposed to caffeine, premature mitosis, characterized by chromosome pulverization, was observed. These results suggest that the suppression of proliferation in high-pressure-treated MEL cells is associated with G2 arrest following S phase delay. Thus, it seems valuable to apply high pressure to the investigation of the cell cycle.