The effects of intramuscular and intravenous sincalide on gallbladder contraction and visualization of the bile ducts were compared in a group of 37 subjects referred for oral cholecystography. The maximum reduction in gallbladder size observed after sincalide 400 ng/kg intramuscular, 54.7 +/- 7.2% (mean +/- SEM), occurred 25 min after injection and was significantly greater than that observed after sincalide 20 ng/kg intravenous, 26.5 +/- 8.2%. Maximum reduction after sincalide 100 ng/kg intramuscular was 47.3 +/- 8.2%. The common bile duct was visualized in 60 and 45% of subjects after intramuscular and intravenous sincalide, respectively. The use of intramuscular sincalide 400 ng/kg intramuscular is an effective and convenient adjunct to oral cholecystography when significant gallbladder contraction and visualization of the common bile duct is desired.