Biliary stents are liable to clog. We investigated whether a choleretic plus an antibiotic could delay clogging. 20 consecutive patients with a malignant biliary stricture were randomised after endoscopic insertion of a polyethylene stent to receive ursodeoxycholic acid plus norfloxacin (13-15 mg/kg and 400 mg, daily) or conservative treatment. The drug combination was associated with: a longer median patency of first (49 vs 6 weeks) and all stents (38 vs 7 weeks); a prolonged median survival (67 vs 18 weeks); and a shorter mean hospital stay (0.2 vs 1.0 days per week of survival). Thus ursodeoxycholic acid plus norfloxacin may prevent stent clogging.