In an open-label prospective study the safety, efficacy, and patient tolerance of an enterally administered isotonic intestinal lavage solution containing polyethylene glycol-3350 was evaluated in 20 pediatric patients (ages 1 1/2 to 19 years) undergoing diagnostic colonoscopy. After an oral dose of metoclopramide, lavage solution was administered by mouth or nasogastric tube at a rate of 40 ml/kg per hour until stools were clear. Emesis occurred in 4 patients, nausea in 11, and abdominal distension in 5. Clear stools were produced in a mean (+/- SE) time of 2.6 +/- 0.3 hours. The volume of lavage solution delivered, which ranged from 15.6 to 183.3 ml/kg, varied inversely with the weight (and age) of the patient. Preparation of the colon was considered optimal in 11 patients, satisfactory in 7, and suboptimal in 2. Small but significant decreases in urine osmolality, blood urea nitrogen, serum glucose, and potassium values were noted at the termination of perfusion. Postperfusion serum glucose concentration in the smallest patient (11.4 kg) was 61 mg/dL (3.4 mmol/L). Mean (+/- SEM) change in weight after perfusion was 0.14 +/- 0.05 kg (range -0.2 to +0.6 kg). Of 20 patients, 11 required or requested nasogastric administration of the lavage solution because of its unpleasant taste. We conclude that whole intestinal perfusion with a balanced electrolyte solution containing polyethylene glycol is safe, acceptable, and efficacious in children.