A new design of endoprosthesis, made of shape-memory nitinol alloy, was used to replace the currently used one, which was soon clogged with bile mud. After nitinol wire coil stent was slenderized in ice water, it was inserted into the strictured bile duct by endoscopy or operation. When nitinol wire coil was positioned in a narrowed biliary segment, normal saline heated to 39 degrees C was rapidly hand-injected into the lumen of the inner transport catheter to make the alloy coil to resume its original shape with a length of 3 to 10cm, and a diameter of 5 to 10mm. Since June 1991, 13 patients with malignant biliary strictures were treated with nitinol endoprosthesis. The follow-up period ranged from 1 to 16 months (average 6 months). Biliary sludge was not found in the endoprosthesis during the period. The results suggested that shape-memory nitinol alloy endoprosthesis could maintain long term patency without severe infection or obstruction due to biliary sludge.