To investigate the effects of pneumoperitoneum on the peritoneal defense mechanism induced by streptozocin infusion during laparoscopic surgery in diabetic rats and to show the importance of regulation of diabetes for peritoneal defense mechanisms. One hundred twenty-six Sprague-Dawley male rats were allocated into six groups each consisting of 21 rats: group 1, nondiabetic sham laparotomy (control); group 2, nondiabetic pneumoperitoneum (control); group 3, uncontrolled diabetes plus sham laparotomy; group 4, controlled diabetes plus sham laparotomy; group 5, uncontrolled diabetes plus pneumoperitoneum; and group 6, controlled diabetes plus pneumoperitoneum. Diabetes was constituted by intraperitoneal infusion of one dose of 60 mg/kg streptozotocin, and diabetes was regulated (in groups 4 and 6) by subcutaneous injection of 10 IU/kg insulin in the morning and evening after the blood glucose measurements since the fourth day. Peritoneal fluid samples were taken at the zero, second, and sixth hours after sham laparotomy for groups 1, 3, and 4 and after pneumoperitoneum for groups 2, 5, and 6 on the seventh day. Total peritonea] cell count, antibacterial activity of the peritoneal fluid, and types of phagocytic cells in the peritoneal fluid were assessed. Peritoneal cell count was found to be lower in uncontrolled diabetes due to high blood glucose levels (>200 mg/dL), which led to slow migration of phagocytic cells into the peritoneum. Pneumoperitoneum had augmented the effect on phagocytic cell migration to the peritoneum compared with the sham laparotomy in controlled diabetic rats. Uncontrolled and controlled diabetes have adverse effects on peritoneal defense mechanism killing functions by interfering with the antimicrobial activity of peritoneal fluid.