From April 89 to October 90, 41 patients operated for a Dukes B or C colorectal cancer were randomized to receive 6 courses of adjuvant treatment with (A) 5-FU alone (440 mg/m2 IV bolus 5/21 days) or (B) folinic acid (200 mg/m2 IV bolus 5/21 days) preceding 5-FU (370 mg/m2 in short infusion 5/21 days). Ten patients received also one course of immediate post-operative continuous portal infusion (5-FU 500 mg/m2/day x 7 followed by a 2 hours infusion of mitomycin C 10 mg/m2). The portal treatment was well tolerated (1 case of GI tract disturbances, 1 catheter obstruction). The toxicity of adjuvant systemic treatment was evaluated on 232 courses (125 A, 107 B). Hematologic and skin toxicities, alopecia and nausea-vomiting were mild. The limiting toxicities (expressed as percentages of courses) were stomatitis (grades 2-3: 11.4% A; 22.6% B) and diarrhea (grades 3-4: 7.3% A; 14.2% B; one toxic death was to deplore in arm B from a grade 4 diarrhea). The pilot study has demonstrated the feasibility of the adjuvant treatment proposed; a multicentric randomized trial (expected accrual: 800 patients) has therefore been activated on 11.01.90; all patients will also receive levamisole while radio-therapy will be mandatory for rectal cancer.