A Gastrointestinal Tumor Study Group (GITSG) protocol showed a survival benefit for patients with locally advanced unresectable pancreatic adenocarcinoma when treated with split-course radiation therapy and bolus intravenous (i.v.) 5-fluorouracil (5-FU) as compared with survival achieved with radiation alone. In an attempt to improve these results, a phase II trial using intraarterial (i.a.) cisplatin, systemic-infusional 5-FU, and concomitant split-course radiation therapy was conducted. Sixteen previously untreated patients with unresectable pancreatic adenocarcinoma (5 with American Joint Committee on Cancer [AJCC] stage I-II, 11 with stage III) disease were treated with i.a. cisplatin 100 mg/m2 by selective celiac arteriography followed by i.v. infusional 5-FU 1,000 mg/m2/day for 4 days, and concomitant split-course external beam photon radiation therapy at 2.0 Gy for 10 days in a 12-day period. After a planned 14-day interval, the identical chemoradiation treatment was repeated; finally, after a second 2-week interval, a third cycle of chemotherapy with a final 10 Gy radiation was administered. All 16 patients were evaluable for response; there were two partial responses (PR: 12%) and five minor responses (31%). Median follow-up period was 77 months. Median time to progression was 6 months (range 1-12 months), and median survival was 9 months (range 4-94 months). Nausea/vomiting was the major toxicity. There were no treatment-related fatalities. This regimen of concomitant i.a. cisplatin, i.v. infusional 5-FU, and split-course external beam photon radiation is well tolerated but has minimal activity in the treatment of locally advanced unresectable pancreatic adenocarcinoma. Future combined-modality protocols for this disease should explore alternative chemoradiation schemes.