Gallbladder stasis may be an important factor in the pathogenesis of cholesterol-gallstone formation in some individuals. We investigated gallbladder function in a group of nondieting, gallstone-free, healthy subjects with normal (22 ± 1 kg/m2) and high (36 ± 1 kg/m2) body mass indexes. Fasting gallbladder volume (28.2 ± 4.4 ml) and residual volume after maximal emptying (8.4 ± 2.3 ml) in high–body-mass index subjects were not significantly different from those of normal–body-mass index subjects (20.5 ± 2.5 ml and 4.2 ± 1.3 ml, respectively). The percentage of gallbladder emptying (71% ± 5%) and the rate of gallbladder emptying (-1.9 ± 0.3 × 10−2 min−1) in high–body-mass index subjects in response to a maximal emptying stimulus was similar to the percentage of emptying (78% ± 6%) and rate of emptying (−2.3 ± 0.6 × 10−2 min−1) in normal–body-mass index subjects. A liquid meal containing less than 1 gm fat, 14 gm protein and 6 gm carbohydrate resulted in both a decreased rate of gallbladder emptying and an increased residual gallbladder emptying and an increased residual gallbladder volume in both groups. The addition of 10 or 20 gm (but not 4 gm) of fat to the liquid meal restored gallbladder emptying to the maximal-stimulus level. These results demonstrate that gallbladder emptying in response to a single liquid meal stimulus is not altered in obesity and that dose-response relationships to fat are similar in obese and normal-weight individuals. Furthermore, these findings suggest that a threshold quantity of fat–no more than 10 gm–included in a liquid-meal stimulus might be able to restore gallbladder emptying to normal. It does not appear that an intrinsic defect in gallbladder contractility is responsible for the increased incidence of gallstones in obesity. (HEPATOLOGY 1992;15:795–798).