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A previous study has shown barium is instilled in the left lateral position or the prone position. However, we previously reported that the colonoscope can be readily inserted into the descending colon in the left semiprone position. Indeed, when the colonoscope was inserted in the left semiprone position, the lumen of the sigmoid colon was observed linearly and the colon position lowered toward the oral side. In addition, it was often observed that the rectosigmoid colon nearly overlapped with the sigmoid-descending colon junction when the patient was placed in the left semiprone position in the single-contrast enema examination. Therefore, we considered that the rectosigmoid colon is located in the highest position while the sigmoid-descending colon junction is located in the lowest position and various kinds of drugs can be readily administered into the proximal colon in the left semiprone position. Our new barium instillation method was devised and this method was performed to determine whether barium can be readily instilled into the proximal colon. Barium (300 ml) passed the hepatic flexure before air insufflation in 32 (67%) of the 48 patients by using our new barium instillation method. By contrast, barium (300 ml) passed the hepatic flexure before air insufflation in 3 (6%) of the 48 patients by using our conventional barium instillation method. These results suggest that effective rectal administration is possible by using our new barium instillation method compared with our conventional barium instillation method.