BACKGROUND Based on encouraging treatment results with FU/FA or FU/IFN in gastrointestinal tract cancer, a phase II study was conducted to evaluate the effects and toxicity of combination FU/FA/IFN in patients (pts) with inoperable/metastatic gastric cancer. METHODS IFN 6 M.U. s.c. 1 x/week, FU 500 mg/m2 bolus i.v. 1 x/week and FA 500 mg/m2 1 x/week as a 2-hour infusion. Of 72 treated pts, 72 (22 females, 50 males) are evaluable for response and toxicity. Median age was 55.6 years (28-80), and median Karnofsky performance status was 80% (70-100). Sites of measurable disease were inoperable primary tumors/local recurrence (18), liver metastasis (22), lymph nodes (31) and peritoneum (20). One pt had bone marrow metastasis and another had paraneoplastic hyperfibrinolytic coagulopathy. RESULTS 10/72 pts had complete response, 20/72 pts partial response, 40/72 pts tumor stabilization and 2/72 pts progressive disease. The median duration of response (CR/PR) was 9 months, the median progression-free interval 6 months, the median survival time was 9 months, and for responding patients (CR/PR) 12.5 months. RESULTS 1/72 pts had WHO grade 4 toxicity (diarrhea), 5/72 pts had WHO grade 3 toxicity (nausea 1, diarrhea 4). Except for 1 treatment-limiting grade 4 toxicity, no modifications of dose or schedule due to toxicity were required. Thirty-six of 44 pts experienced a significant reduction in tumor-related pain under treatment. CONCLUSIONS Biochemical modulation of FU with FA and IFN is effective in advanced gastric cancer. Moderate toxicity, outpatient treatment setting and high rates of amelioration tumor-related pain contribute to an effective palliation.