Objective    To study the effects of carbon dioxide or helium pneumoperitoneum on the human gastric cancer cells in terms of proliferation and to provide evidence for the safety of CO

2

pneumoperitoneum in laparoscopic radical distal gastrectomy.     Methods    The cultured gastric cancer cell line MKN-45 was exposed to CO

2

or helium environment maintained at 12 mmHg for 3 h. The cells exposed to 5% CO

2

at 37 ℃ served as control. In every half an hour during 3-hour exposure

the pH value of culture media was measured. On each day in the following week afte

r exposure

the proliferation of MKN-45 was examined by MTT method.     Results    The pH value of culture media was a little bit lower than 7 after exposed to CO

2

environment

significantly different with that of control group (P0.01)

but it recovered to normal levels 2 h later. The pH value of helium group was a little bit higher than 7

significantly different with that of control group (P0.05)

then down to normal level in 1.5 h. MTT results showed the proliferation of MKN-45 cells showed no significant difference among CO

2

group

helium group and control group (P0.05).     Conclusion    Simulated CO

2

or He pneumoperitoneum at 12 mmHg does not affect the proliferation of gastric cancer cells MKN-45 in vitro.