After surgery, patients with stage I, stage IIA, or stage IV colon cancer are immediately removed from study. Patients with stage IIB, IIC, or III colon cancer are re-registered within 35 days postoperatively. Beginning 21-35 days after surgery, patients with stage IIC or III disease receive leucovorin calcium IV bolus immediately followed by 5-FU IV bolus on days 1-5. Courses repeat every 28 days for a total of 6 courses in the absence of disease progression or unacceptable toxicity. Patients with stage IIB disease do not receive adjuvant 5-FU and leucovorin calcium.