The purpose of this study was to demonstrate that polyethylene glycol electrolyte lavage solution (PEG-ELS), a colonic lavage solution presently used for gut cleansing in preparation for colonic procedures, can be an effective agent in the treatment of chronic constipation. Thirty-two patients with chronic constipation completed a controlled, double-blind, randomized, cross-over study. Each patient was given two containers, marked A and B, one containing PEG-ELS and the other a placebo. They drank a specified amount (8 or 16 oz) of solution A for five consecutive days. Daily number of bowel movements and stool consistency were recorded. Group I (patients 1-16) drank 8 oz of solution per day; group II (patients 17-32) drank 16 oz of solution per day. Mean stool frequency and mean stool consistency were calculated per 5-day testing period for each treatment group (8 oz placebo, 8 oz PEG-ELS, 16 oz placebo, 16 oz PEG-ELS). Two-factor analysis of variance results confirmed that PEG-ELS was superior to placebo with regard to mean stool frequency (7.75 +/- 4.55 vs. 4.88 +/- 2.62, p less than 0.01) and mean stool consistency (2.56 +/- 1.17 vs. 1.91 +/- 0.94, p less than 0.05). Furthermore, PEG-ELS 16 oz per day was superior to all other groups with regard to the measured variables. Side effects from the PEG-ELS were infrequent and tolerable. Our results indicate that PEG-ELS may be an effective alternative therapy in the treatment of chronic constipation. The proper dosage is probably between 8 and 16 oz per day.