Data are presented from 1,166 patients with Dukes B and C carcinoma of the colon who were entered into the National Surgical Adjuvant Breast and Bowel Project (NSABP) Protocol C-01 between November 1977 and February 1983. Patients were randomized to one of three therapeutic categories: 1) no further treatment following curative resection (394 patients); 2) postoperative chemotherapy consisting of 5-fluorouracil, semustine, and vincristine (379 patients); or 3) postoperative BCG (393 patients). The average time on study was 77.3 months. A comparison between patients receiving postoperative adjuvant chemotherapy and those treated with surgery alone indicated that there was an overall improvement in disease-free survival (P = .02) and survival (P = .05) in favor of the chemotherapy-treated group. At 5 years of follow-up, patients treated with surgery alone were at 1.29 times the risk of developing a treatment failure and at 1.31 times the likelihood of dying as were similar patients treated with combination adjuvant chemotherapy. Comparison of the BCG-treated group with the group treated with surgery alone indicated that there was no statistically significant difference in disease-free survival (P = .09). There was, however, a survival advantage in favor of the BCG-treated group (P = .03). At 5 years of follow-up, patients randomized to the surgery-alone arm were at 1.28 times the risk of dying as were similar patients treated with BCG. Further investigation disclosed that this survival advantage in favor of BCG was a result of a diminution in deaths that were non-cancer related. When analyses were conducted on which events not related to cancer recurrence were eliminated, the survival difference between the BCG and control groups became nonsignificant (P = .40); the cumulative odds at 5 years decreased from 1.28 to 1.10. The findings from this study are the first from a randomized prospective clinical trial to demonstrate that a significant disease-free survival and survival benefit can be achieved with postoperative adjuvant chemotherapy in patients with Dukes B and C carcinoma of the colon who have undergone curative resection.