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 x 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 x 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.(ABSTRACT TRUNCATED AT 250 WORDS)