After curative resection (R-0) of primary colon cancer or curative metastases resection, the efficacy, toxicity and compliance of a weekly 24-h infusion of high-dose 5-FU with folinic acid was examined in a prospective feasibility trial. From June 1995 to June 1997, 19 patients were included, 11 patients with UICC stage III and 8 patients with UICC stage IV colon cancer. The patients received weekly 500 mg/m2 of calcium folinic acid (Rescuvolin) as a 1-2 h-infusion on an outpatient basis following a 24-h infusion of 2,000 mg/m2 5-FU via a pump system (intermate LV5 Baxter). The adjuvant therapy was administered for 6 months. 90% of the patients received the planned 18 chemotherapy applications. The total 5-FU dose given to each patient amounted to 34.4 g/m2 in 6 months, thus corresponding to 95% of the planned 5-FU total dose. The main toxicity was diarrhea CTC toxicity grade 3 in the case of 16% of the patients. After a median follow-up of 51 months (range: 37-59 months), 82% of the patients (9 out of 11) with stage III remained free of recurrence. The 2 cases of recurrence belonged to the pN2 subgroup. In stage IV only 12% of the patients (1 out of 8) remained free of recurrence. On an adjuvant basis, a weekly 24-h infusion of high-dose 5-FU with folinic acid is accompanied by a good complicance and a high-dose intensity of 5-FU. Now it is tested within randomized phase III trials of the "Arbeitsgemeinschaft Gastroenterologische Onkologie (AGO)" of the "Deutsche Gesellschaft für Verdauungs- und Stoffwechselerkrankungen" for UICC stage III colon cancer. Concerning stage IV, adjuvant therapy was not effective, a fact that seems to justify new drugs and new therapeutic strategies.