Light food diet and low residual diet with hydration, both combined with Proctosal and Bisacodyl cleansing, were compared in 268 patients in the preparation of the colon for double contrast examination. Low residual diet with hydration resulted in significantly less residual fecal material, no flocculation of the barium coating and significantly denser mucosal coating. The examination had to be repeated more often (8.6%) after light food diet than after low residual diet with hydration (1.7%), but there was no statistically significant difference in the diagnostic accuracy. The hydration is important in avoiding patient discomforts and flocculation of the barium coating. Despite the use of laxatives, a strict diet restriction is needed to obtain consistently clean colon.