Background: The high volume and poor palatability of standard colon cleansers remain obstacles to colonoscopy for many patients. Significant electrolyte disturbances and fluid balance alterations may occur with available agents. L-glucose, the stereoisomer of D-glucose, has laxative effects that make it potentially useful as a colon-cleansing agent. This study evaluated the safety and efficacy of L-glucose as a bowel cleanser before colonoscopy. Methods: Thirty healthy individuals (age range 34-70 years) scheduled to undergo outpatient colonoscopy were given 24 g of L-glucose in 8 ounces of water to cleanse the colon. Nonblinded endoscopists rated the quality of the preparation based on established criteria. Laboratory studies were monitored before and after administration of the L-glucose and on the day after colonoscopy; adverse clinical events were also monitored. Results: L-glucose administration resulted in excellent or good preparations in 80% (24/30) of the patients and fair or poor preparations in 20%. Average water consumption was 48 ounces. No adverse event occurred, and no significant laboratory test abnormalities were identified. Conclusions: Eighty percent of patients who prepared for colonoscopy by ingestion of L-glucose had good or excellent preparations. The L-glucose preparation was palatable, and its efficacy and safety appear equivalent to currently available colon-cleansing agents. (Gastrointest Endosc 2003;58:30-5.)