One hundred and sixty patients were enrolled in a double-blind, placebo-controlled trial to evaluate the effectiveness of the combination of the polyethylene glycol electrolyte lavage solution GoLYTELY (Braintree Laboratories, Inc., Braintree, MA, U.S.A.) and the contact laxative bisacodyl (Dulcolax, Boehringer Ingelheim Pharmaceuticals, Ridgefield, CT, U.S.A.) in improving outpatient preparation for colonoscopy. One hundred and fourteen patients completed the study; 59 received GoLYTELY followed by three Dulcolax capsules and 55 received GoLYTELY followed by three placebo capsules. A statistically significant improvement in the group receiving Dulcolax was noted in overall quality of preparation (p = 0.015) and amount of liquid stool present during colonoscopy (p = 0.02). We noted no significant difference in the occurrence of adverse effects. No patient in either group suffered from symptomatic orthostatic hypotension. These results suggest that an improved colonoscopy preparation can be obtained by combining a standard GoLYTELY preparation with three 5-mg Dulcolax tablets, without sacrificing patient safety or comfort.