We report a well tolerated endoscopic technique of administering intraluminal radiotherapy to 14 patients with inoperable cholangiocarcinoma, in which the iridium-192 wire source was inserted down a nasobiliary catheter placed within a previously inserted endoscopic biliary prosthesis, thus allowing bile flow to continue during treatment. Radiotherapy was commenced 2 weeks after biliary decompression, when the median serum bilirubin level had fallen from 213 to 34 mumol/l. A total radiation dose of 6000 cGy at 0.5 cm from the source was administered over a median of 85 h (range 77-116 h). In four patients there was a transient increase in serum bilirubin during iridium treatment and, in two cases (14 per cent), this was associated with mild cholangitis. Both cases resolved rapidly once the iridium wire and nasobiliary catheter were removed. The median hospital stay after treatment was 2.5 days (range 0-28 days). The late complications associated with stent blockage were minimized by routinely changing stents at 4-6 monthly intervals; ten of the patients have so far undergone from one to five (median three) stent changes. Five patients have died at 3.6-8.2 months (median 4.8 months) following iridium treatment; four had extensive type III hilar lesions at diagnosis. Nine patients are still alive at 5.4-31.0 months (median 16.4 months). The overall median survival after iridium therapy is 10.5 months. This technique of endoscopic biliary decompression before internal iridium administration minimizes complications by allowing biliary drainage during treatment. The role of this treatment in patients with inoperable cholangiocarcinoma awaits the results of randomized, controlled trials.