In a prospective study, we investigated the effect of extracorporeal shock-wave lithotripsy (ESWL) on gallbladder contractility and on fasting and residual gallbladder volume in patients with solitary and multiple gallbladder stones with stone densities < 100 Hounsfield units (HU) and adequate gallbladder function. Twenty-five patients (seven males and 18 females, mean age 48.5 +/- 11.7 years) treated with ESWL were assigned to either group I, consisting of 13 patients with solitary stones < 20 mm diameter, or group II, including patients with two to three stones and maximum stone diameter of 30 mm. ESWL was performed with the MPL 9000 lithotripter. Gallbladder ejection fraction was determined using the method of Dodds after a 12-hr fast and following application of a standard stimulative meal. Gallbladder volume was measured by ultrasound over 90 min at 10-min intervals before ESWL, then at 1, 30, 120, and 210 days after ESWL. At 24 hr after ESWL, residual gallbladder volume increased in group I from 7.4 ml to 13.9 ml (P = 0.0567) and in group II from 6.5 ml to 20.2 ml (P = 0.0076). Thereafter, residual volumes returned to pre-ESWL levels. In group II, post-ESWL fasting volumes were significantly increased over initial values at all time intervals. Correspondingly, only at 24 hr after ESWL, ejection fractions decreased from 73.1% to 64.9% in group I and from 76.5% to 62.7% in group II. No statistically significant differences in gallbladder contractility between the two groups were observed at any point of the follow-up period.(ABSTRACT TRUNCATED AT 250 WORDS)