The study was conducted in 200 consecutive patients undergoing screening colonoscopies for the detection of early colon cancer. The examinations were performed with Olympus 165 colonoscopes by seven experienced endoscopists, each of whom performed alone about over 2000 colonoscopies. The patients were randomly assigned to Group I and II with either air or carbon dioxide insufflation. Both study groups were matched by sex, age, duration of the procedure, and BMI. The authors compared for the duration of the procedure, coecal intubation time, complication rate, pulse rates immediately after the procedure, 15 minutes after, and subjective pain evaluation on a Visual Analogue Scale.