Sludge, which occludes biliary stents, forms mainly around the side-holes of such stents. It has been reported that omitting the side-holes results in less sludge formation and theoretically improves drainage. To compare the clinical efficacy of biliary stents with and without side-holes, we randomized patients with malignant or benign strictures to receive 10FG polyethylene stents either with side-holes (SH) or without side-holes (NSH). The patients were seen at 4, 12, 20, and 28 weeks after stenting for symptom evaluation and serum liver enzyme and bilirubin assays. The stents were replaced only when clinical symptoms of cholangitis developed. Each group included 35 patients. The mean age of patients in the SH group was 68 years, and the ratio of men to women was 1:1.3. In the NSH group, the mean age of patients was 67 years, and the ratio of men to women was 1:1.4. Eight patients with SH stents and eight with NSH stents died before the stents were removed; two NSH stents migrated into the duodenum. During a mean follow-up period of 8.1 weeks (range, 1.1 to 28 weeks for the SH group and 0.6 to 28 weeks for the NSH group), 18 stents were found to be occluded in the SH group and 17 in the NSH group. The median time before total occlusion was 7.8 weeks (range, 2.6 to 28) for SH stents and 7.9 weeks (range, 0.6 to 28) for NSH stents (p > 0.1, NS). The occluded stents removed from these patients were freeze-dried and weighed to quantitate the sludge blocking the stent lumen.(ABSTRACT TRUNCATED AT 250 WORDS)