The effects of i.p. CO2 insufflation on bacterial proliferation in a setting of Escherichia coli-induced experimental peritonitis was studied in a rat model. Six male Wistar rats were given 0.25 ml of i.p. saline and formed the sham operation group. Twenty-four rats were divided into three groups, and all had i.p. E, coli injections. Microorganism counts were taken after 8 h in ail groups. Group I was used as the control group. Group 2 (laparoscopy) was insufflated with CO2, and group 3 (laparotomy) had a midline laparotomy. Microorganism counts were repeated 8 h after the procedures (16 h after i.p. E. coli inoculation). Postoperative microorganism counts were significantly higher in the CO2 insufflation group (p < 0.05) compared with the control and laparotomy groups and showed an increase, whereas they decreased in the other two groups.