Colonoscopy preparation with lavage is a clinically accepted procedure. After having shown that its results can be improved by the additional intake of Senna this randomized prospective trial was designed to evaluate the effects of different laxatives in a combined preparation regimen. The day before endoscopy either Bisacodyl or extractum Sennae was given to 120 patients. Immediately before examination all patients underwent whole gut irrigation with Golytely solution. Patient acceptance and effectiveness of the two procedures were excellent and no relevant intolerance was observed. Satisfactory cleansing results were achieved with Bisacodyl as well as with Senna (98.3 vs. 95%). There was no significant difference between the laxatives used. We conclude that both regimens are safe, generally well tolerated and effective ways of preparation for colonoscopy.