Objective: The aim of this prospective study was to examine the effects of intraperitoneal C02 insufflation on ETC02 and blood gases during laparoscopic cholecystectomies.Methods: Twenty patients ASA I,II, aged 20-65 years were studied. After induction, anesthesia was maintained with 1% isoflurane in 70% N20 and 02. Vecuronium bromide was administered for muscle relaxation and all patients were ventilated mechanically with 10ml/kg tidal volume and 10 / min respiratory rate. Mean arterial pressure, heart rate, ETC02, Sp02 and peak airway pressure were measured before and after 002 insufflation, at 5 minutes intervals and blood gases at 15 minutes intervals during operation.Results: The peak airway pressure and mean arterial pressure increased immediately after C02 insufflation. ETC02 increased significantly at 5th minute of C02 insufflation. At 15th minute PaC02 increased and pH decreased significantly. A plateau was reached ten minutes later and remained constant during operation. No significant differences were observed in 02 saturation,heart rate and Pa02 values.Conclusion: Intraperitoneal C02 insufflation causes significant increases in ETC02, PaCo2, peak airway pressure and decreases in pH.