To determine whether the site of gas sampling affects end-tidal gas measurements in adult patients during anesthesia, end-tidal pCO2(PetCO2) was measuredcontinuously from the distal and proximal ends of the endotracheal tube(SHERIDAN) in 33 adults ventilated with Drager anesthesia ventilator. These data were compared with simultaneous arterial PCO2 (PaCO2) measurements. The study was commenced after each patients was ventilated no less than 15 minutes at the desired ventilator settings. Gas was continuously aspirated at 230 ml/min. for measurement of the PetCO2 using SARA Cap.A.G,Capnometer'sampled from the distal and proximal ends of the endotracheal tube for 3-minutes of each sampling port, alternativiely measured at 5 minutes interval. And each measurement was repeated twice and calculated mean values. The results were as follows: The mean PetCO2 sampling from the distal end was 31.6±2.4 mmHg. and the proximal end was 31.0±2.3mmHg. The difference between two results was statistically not significant(p> 0.05). The correlation coefficients of PetCO2 vslues for the distal end and the proximal end samplings to the PaCO2 values were r =0.48 and r=0.45 respectively, and statistically significant(p< 0.05) We concluded that the measured PetCO2 sampled from the distal end of the ETCO cuffed endotracheal tube' does not show any statistically significance to the proximal one. However, distally sampled PetCO2 measurements were more approximate PaCO2 measurements than proximally sampled one.