In experimental animals, sphincterotomy facilitates passage of solids from the gallbladder and inhibits gallstone formation apparently by improvement in gallbladder emptying. In humans, however, gallbladder emptying has not been studied following endoscopic sphincterotomy (ES) in patients with gallstones. We therefore prospectively studied resting and cerulin-stimulated gallbladder volumes by real time ultrasonography in 15 patients of choledocholithiasis with gallbladder in situ (eight with and seven without gallbladder calculi) before and after (after bile duct clearance) ES. ES significantly lowered resting gallbladder volume (21.2 +/- 10.6 vs 11.1 +/- 5.0; P < 0.0001) and cerulin-stimulated residual gallbladder volume (10.8 +/- 5.6 vs 4.4 +/- 2.1; P < 0.0001). ES also significantly increased the gallbladder ejection fraction (47.3 +/- 12.1% vs 58.8 +/- 11.1%; P < 0.0001). The rate constant for gallbladder emptying after cerulin infusion also increased significantly after ES (-0.022/min vs -0.031/ min; P < 0.0001). Significant improvement in gallbladder motility was observed in both groups of patients with and without gallbladder calculi. ES significantly improves gallbladder motility in humans.