Background:  Endoscopic insertion of biliary stents is a useful treatment for obstructive jaundice resulting from unresectable tumors of the pancreas and biliary tree. The main drawback is the recurrence of jaundice due to clogging. The aim of this study was to establish an experimental model of polyethylene stent clogging in large white pigs. Methods:  A straight polyethylene stent of 5F (group I), 7F (group II) or 10F size (group III) was inserted in the common bile duct. Animals were killed at 2 months, or earlier if physical signs suggesting stent clogging occurred. Chemicophysical analysis of stent deposition combined stereomicroscopy and identification of the contents by means of Fourrier transform infrared spectroscopy. Bacteriologic analyses included identification of aerobic and anaerobic bacteria and measurement of β-glucuronidase, lecithinase and lipase activities. Results:  Physical signs suggesting stent obstruction or death occurred in 8 of 8 animals in group I, 11 of 12 in group II, and 2 of 8 in group III (p < 0.001). The proportion of mucoprotein in the stent contents tended to fall with increasing stent diameter (mean 82%, 58% and 47% for 5F, 7F and 10F, respectively), whereas wheat starch and calcium bilirubinate content increased with increasing stent diameter (9% and 4%, 18% and 10%, and 29% and 23% for 5F, 7 F, and 10F, respectively), although none of these differences were statistically significant. A variety of bacteria were cultured from the stent deposits, including anaerobic strains. Clostridium species were associated with the highest enzyme activities. Conclusions:  In this model the major component of early stent deposits was mucoprotein, and numerous aerobic and anaerobic bacteria were isolated. Formation of calcium bilirubinate was a late phenomenon and poorly related to bacterial enzymatic activities. (Gastrointest Endosc 2000;51:12-8.)