At the end of extracorporeal shockwave lithotripsy (ESWL) gallstone fragments are dispersed throughout the gall-bladder. In this state they should be expelled more easily than when later sedimented to the gall-bladder fundus. Thus, a randomized study was performed to evaluate the clinical benefit of induced gall-bladder contraction after ESWL. One hundred and five patients with radiolucent gallstones (1-3 stones, diameter < or = 30 mm) were randomized to received either saline or an infusion of 0.2 micrograms/kg ceruletide. Stone clearance rates and incidence of biliary symptoms were recorded. Clearance rates at 6 weeks and 3 months after ESWL were significantly (P < 0.025) improved by the ceruletide infusion. This effect, resulting in shortened bile acid therapy, was limited to patients with small solitary stones and dependent on a good initial fragmentation. Major side effects attributable to ceruletide were not observed. These results suggest that induced gall-bladder contraction can be successfully applied as an adjuvant treatment in a subgroup of patients with small solitary gallstones.