The effectiveness and acceptability of three colon cleansing regimens for colonoscopy were compared in a prospective study in 271 patients stratified as in- and out-patients and randomly assigned to either I) a diet and Senna laxative (X-prep), combined with a saline enema (n = 88); II) 41 of a polyethylene glycol electrolyte lavage solution (Golytely) (n = 90); or III) a combined regimen of Cascara-Salax laxative (PicoSalax) and 1.51 Golytely (n = 93). Patients and colonoscopists indicated independently their overall impression of palatability and convenience and the completeness of the preparation, respectively, on 0- to 10-cm visual analogue scales. No differences were found between the regimens, either for the patients' impression of palatability or for the convenience of the preparation. A significantly cleaner colon was obtained with regimen II in outpatients than with regimen I (p = 0.02), whereas no differences were found either between regimens I and III or between regimens II and III. With regimen I, II, and III, 14%, 8%, and 12% of the patients, respectively, had scores indicating inadequate preparation. Outpatients (n = 175) had significantly cleaner colon than inpatients (n = 96) (p less than 0.001). In conclusion, no clinically important differences were found between the three bowel preparation regimens. An oral irrigation regimen is acceptable to the patients and may be preferable because it provides more flexibility to the endoscopic laboratory.