The effect of intravenous and intramuscular administration of ceruletide on gallbladder contraction was investigated in 67 normal volunteers and patients. Of the 45 normal volunteers, 33 received the drug intravenously and 12 intramuscularly in graded ascending doses. By either means of injection, ceruletide produced a substantial contraction of the gallbladder with a measurable reduction in gallbladder area. Based on findings in these groups, the 22 patients requiring oral cholecystography for clinical evaluation received 0.3 microgram/kg intramuscularly. The intramuscular administration of synthetic ceruletide after oral cholecystography, in a dose of 0.o microgram/kg, afforded a safe and effective means of gallbladder contraction, with resultant cystic and common bile duct visualization. Side effects occurred less frequently when the drug was administered intramuscularly and were minimal and self-limiting. Peak contraction (40% or greater reduction in size) occurred as early as 5-15 min after after intramuscular injection and in most instances within 30 min.