The cholecystokinetic effect of ceruletide, a synthetic decapeptide similar in action to cholecystokinin, was examined in both a randomized and nonrandomized study in 81 patients scheduled for routine oral cholecystograms. Intramuscular injection of ceruletide in a dose of 0.3 microgram/kg resulted in a mean maximum contraction of the gallbladder of 68% and a mean time until maximum contraction of 28 minutes. Visualization of the cystic duct occurred in 57 patients (70%); the common duct was seen in 67 (83%). Ceruletide demonstrated superior gallbladder contraction when compared to fatty meals and demonstrated no interference with a subsequent upper gastrointestinal series.