The feasibility of a combined chemotherapy using dipyridamole (DP) with adriamycin (ADM) and 5-fluorouracil (5-FU) was investigated. First, the chemosensitivity of gastric cancer tissues was determined by the succinate dehydrogenase inhibition test, which showed sensitivity to ADM and 5-FU is increased by DP. Next, a clinical trial of combined therapy of DP, ADM and 5-FU, as a post-operative adjuvant chemotherapy for gastric cancer patients, was performed. DP (50 mg) was given as a 1-h i.v. infusion, and ADM (20 mg) was given as a single i.v. injection. This treatment was started on post-operative day 10, and was repeated every 2 weeks. Simultaneously with these treatments, DP (300 mg) and 5-FU (150 mg) were administered post-operatively daily. A total of 63 courses of therapy in nine patients were performed. The adverse effects related to the DP infusion were flushing, headache, nausea and upper abdominal discomfort, all of a low grade. DP did not appear to alter the toxicity of ADM and 5-FU, and no severe adverse effect was noted for this combination therapy. The pharmacokinetics of DP were also investigated in five patients. The mean plasma concentration of DP increased 4.41 micrograms/ml and remained above 0.25 microgram/ml for over 6 h. This combination chemotherapy appears to be safe and may be useful clinically in treating cancer.