The contractile effect of erythromycin on gallbladder has not been fully understood. This effect was investigated in the isolated gallbladder of golden hamster gallstone model and in human by ultrasonography. Erythromycicn induced concentration-dependent contraction of gallbladder in 28 hamsters with normal diet and in 13 with gallstone diet. In those two groups the maximal contractile effect and the half maximal effective concentration were similar (P > 0.05). In clinical study, the fasting volume and residual volume were significantly diminished in 23 volunteers and 15 with cholecystolithiasis and the ejection fraction and the constant emptying rate increased (P < 0.05). Erythromycin also modulated the hypomotility of gallbladder in gallstone patients, hence could be used in gallbladder hypomotility cases.