AIM: To investigate the effects of carbon dioxide (CO2)and helium insufflation administered at different pressures on the growth and apoptosis of cultured human gastric cancer cells.METHODS: The gastric cancer cells MKN-45 were exposed to a CO2 and helium environment maintained at different pressures (0, 5, 10 and 15 mmHg). The cells were exposed to simulated pneumoperitoneum environment for 4 h, and pH of the culture media was measured after it was moved to normal conditions for 0, 2, 4, 6 and 8 h. Proliferation viability of MKN-45 was examined by 3-[4,5Dimethylthiazol-2-yl],5-diphenyltetrazolium bromide or triazolyl blue (MTT) assay after it was moved to normal conditions. Apoptotic ratio was measured by Annexin V-FITC/PI double labelled staining.RESULTS: The pH of media was acid and recovered to normal after 4 h in the CO2 group while it was basic in the helium group. There was no difference between CO2 groups (under 10 mmHg ) and control group (P ＞ 0.05)in the proliferative viability of the cells. The cultured cells exposed to 15 mmHg CO2 environment grew more slowly than control group from 4 to 7 d (P ＜ 0.01 ) while there was no difference from 1 to 3 d (P ＞ 0.05). The proliferative viability in helium group was not obviously different from the control group (P ＞ 0.05). The apoptotic ratio of the cultured cells was markedly higher than that of the control group (P ＜ 0.01) at 10 and 15 mmHg CO2 insufflation pressure. In helium group, the apoptotic ratio was not obviously different from the control group (P ＞ 0.05).CONCLUSION: There is no obvious effect in the proliferation and apoptosis of MKN-45 cells under 10 mmHg CO2 insufflation pressure and helium in any pressure. Fifteen mmHg CO2 insufflation pressure can inhibit the proliferation of the cells and improve apoptosis.