Background: Introduction of a pneumoperitoneum using CO2 is acoompanied by significant alterations in respiratory function and pulmonary ryas exchange during laparoscopic cholecystectomy. Previous studies have shown differing regults concerning pulmonary gas exchange: a significant decrease of PaO2 was induced wish isoflurane. In contrast, no significant changes were observed with propefol. The purpose of the present study was to compare the effects of propofol vs isoflurane on pulmonary gas exchange during general anesthesia fur laparoscopic cholecystectomy. Methods : Forty patiens were divided randomly between isoflurane ailed propfol groups. After induction of anesthesia, ventilation was controlled and intra-abdominal pressure was maintained auto-matically at 12 mmHg by a CO2 insufflator. After the measuring of baseline values of blood pressure, 30min after CO2 insufflation and 5 min after CO2 exsufflation. Results : In the isoflurane group, PaCO2, PetCO2, PaO2, and P(a-et)CO2 changed significantly 30 min after CO2 insufflation and 5 min after CO2 exsufflation (P< 0.05). In the propofol group, PaCO2 and PetCO2 incresed significantly 30 min after CO2 insufflation and f min after CO2 exsufflation (P < 0.05),but PaO2 and P(a-et)CO2 remained constailt. When the two groups were compared, there were significant differences in PaO2, PaCO2, PetCO2 and P(a-et)CO2 at 30min after CO2 insufflation and 5 min after CO2 exsufflation ( P<0.05). Conclusions : These results indicate that during laparoscopic cholecystectomy the PaO2 was significantly lower and PaCO2 and P(a-et)CO2 were significantly higher in the isoflurane group compared with the propofol group. ( Korean J Anesthesiol 2000; 38: 1-7)