A comparison study of 80 patients using either intramuscular ceruletide or a fatty meal to contract the gallbladder after oral cholecystography is described. The maximum mean percentage reduction of the gallbladder area was significantly greater with ceruletide (59%) compared to a fatty meal (29%). At all time intervals, a 40% or more reduction in gallbladder area occurred in a higher percentage of patients receiving ceruletide, with improvement in cystic and/or common duct visualization occurring at an earlier time than with a fatty meal. There were no adverse effects after gallbladder contraction when large or small calculi were present.