Gallbladder stasis has been implicated in gallstone formation. Gallbladder filling and emptying were quantitated by computer-assisted cholescintigraphy in 41 normal subjects versus 26 patients with gallstones. Gallbladder contraction was induced by low-dose (1.2 U/kg· h) cholecystokinin infusion. Gallstone patients exhibited normal gallbladder filling, but emptying was significantly (p< 0.01) reduced compared with controls. On closer inspection, the patients fell into two subgroups, separated by t 1/2, the time to empty 50% of gallbladder contents, 19.1 min (x¯+ 2 SD of control). Fifteen patients (57.7%) with a normal t 1/2 (< 19.1 min) exhibited both normal filling and normal emptying. The remaining 11 patients (43.3%) with t 1/2> 19.1 min had grossly abnormal gallbladder emptying, significantly (p< 0.001) different from both the previous patient subgroup and the controls. There was no significant difference in age, sex, prevalence of obesity, presence or absence of biliary colic, and gallstone size, number, or calcification between these two subgroups. Thus, defective gallbladder emptying is evident in a subgroup of gallstone patients, and is independent of clinical features, stone size, and number. Impaired emptying should be considered when assessing pathogenesis or medical therapy.