Sincalide, a synthetic analog of cholecystokinin capable of stimulating bowel motility, has been administered to 12 patients with symptoms and signs of vincristine-induced ileus. Patients were given intravenous infusions of sincalide 0.01 microgram/kg/h over 2-24 h (mean, 8 h) for 1-12 days (mean, 5 days), usually until all evidence of ileus had resolved. Improvement was noted within 48 h of initiation of therapy in eight patients (75%), whereas marginal or no responses were observed in four patients. The mean duration of ileus was 3.6 days in responders and 7.7 days in nonresponders. Toxicity was minimal and consisted of diarrhea in two patients, in whom symptoms promptly resolved with discontinuation of the drug. Further explorations of this promising agent in the treatment of vincristine-induced ileus appears warranted.