Colonoscopy cleansing regimens were evaluated in 197 patients randomized in two study phases to one of four methods: group 1 (64 patients), 3-day clear liquid diet; group 2 (40 patients), 3-day minimum-residue diet; group 3 (44 patients), 1-day minimum-residue diet; group 4 (49 patients), Golytely. Groups 1-3 also received laxatives and enemas before colonoscopy. Physician assessment by endoscopists unaware of the method of colon cleansing favored group 4 (p less than 0.001), with good to excellent preparations achieved in 69% of group 1, 80% of groups 2 and 3, and 92% of group 4. Group 4 patients also experienced less abdominal distress (p less than 0.01). Breath hydrogen and methane levels were measured in groups 3 and 4 both before and after preparation. The decrease in pre- to postprep levels of hydrogen and methane were not significantly different between the groups and postprep gas concentrations were below combustible levels in both groups. There were no clinically significant differences between the four groups for any of the other measured hematologic or biochemical parameters. It is concluded that Golytely is a safe, effective method of colon cleansing, well tolerated by patients.