Previous studies indicate that photodynamic therapy provides effective relief from biliary obstruction in advanced cholangiocarcinoma. This report describes a method of applying photodynamic therapy in the biliary tract by using accessories available in the United States. Endoscopic retrograde cholangiography was performed to define the proximal and distal extent of intraductal tumor. Patients were injected with 2 mg/kg of sodium porfimer. Forty-eight hours later a commercially available cylindrical diffusing laser fiber was inserted into an 8F biliary catheter equipped with a 0.038 inch side-hole at its distal tip. After positioning of a 0.035 inch guidewire proximal to the biliary stricture, the preloaded catheter was advanced over the guidewire by using the monorail technique. Laser light was applied at a power of 400 mW/cm fiber for a total energy of 180 J/cm.2 Fourteen treatments were performed on 6 patients with tumors of Bismuth types IV (n = 2), III (n = 3), or II (n = 1). By using the preloaded biliary catheter, adequate positioning of the laser fiber was achieved in all patients. A fracture of the diffuser tip occurred during 1 of the treatments.Two patients developed acute cholangitis and 2 patients experienced skin phototoxicity. Photodynamic therapy for cholangiocarcinoma is safe and technically feasible with a preloaded biliary catheter and a monorail technique for catheter positioning.