During laparoscopic surgery, gases such as carbon dioxide (CO(2)), helium, or normal air are insufflated into the intra-abdominal cavity so the surgeon can obtain a clear surgical field; however, this insufflation technique may cause injury to the intra-abdominal organs. This study was undertaken to evaluate the effects of different pressures of CO(2) on the apoptotic index in the peritoneum during laparoscopic surgery. A total of 30 Sprague-Dawley male rats were used in the study. CO(2) was insufflated into the intra-abdominal cavity via an angiocatheter cannula by an insufflator at pressures of 10 and 20 mm Hg over 60 min. In the control group, the cannula was inserted into the intra-abdominal cavity, but no gas was insufflated. After 60 min, the rats were killed; peritoneum was harvested from the abdominal wall and was cultured in the cell culture laboratory. Apoptotic and living cells were detected immunohistochemically, and the apoptotic index was calculated and statistically analyzed. The data collected revealed that the apoptotic index increases in proportion to the level of CO(2) pressure. CO(2) pneumoperitoneum is a very useful technique. Gas pressure must be carefully set during the operation, however, or injured mesothelial cells may cause serious malfunction.