To establish the effectiveness of adjuvant chemotherapy in patients with colon cancer after radical surgery, from 1980 to December 1983, 263 patients were randomized in a multicentric study to no further treatment (131 patients) or to a combination of fluorouracil (5-FU) (400 mg/m2 i.v., days 1-5) and lomustine (CCNU) (100 mg/m2 per os on day 5) every 6 weeks for 9 cycles (132 patients). The two groups were well balanced for age, sex, histology, tumor and nodal extent. Chemotherapy was not given to 30 of the 132 randomized patients, and of 98 treated patients only 38 completed the entire protocol. Analysis, as intention to treat, at 54 months did not show any significant difference between the two treatment groups in terms of relapse-free survival (surgery alone, 74.5%; surgery + adjuvant chemotherapy, 70.9%; p = 0.91). In contrast, a significant difference was observed in overall survival (surgery alone, 78.8%; surgery + adjuvant chemotherapy, 60.8%; p = 0.04). The sites of relapse were identical in the two treatment arms. In conclusion, from this study it appears that adjuvant chemotherapy with 5-FU and CCNU seems to have no efficacy in the cure rate of colon cancer patients.