A prospective, randomized trial of adjuvant portal infusion of 5-fluorouracil in combination with mitomycin C was conducted on 469 patients with operable colorectal cancer. A single postoperative course of the cytotoxic agents was compared with radical surgery alone. The actuarial 5-year survival (median follow-up 48 months) was 70 +/- 3% in the chemotherapy group and 57 +/- 4% in the control group (p = 0.10). The respective figures for disease-free survival were 62 +/- 4% and 53 +/- 4% (p = 0.09). Among the 195 cases with strict adherence to the protocol for adjuvant chemotherapy there were 59 recurrences and 44 deaths in the follow-up period, whereas in the 274 with no or incomplete chemotherapy there were 120 recurrences and 99 deaths (p less than 0.05). Perioperative adjuvant chemotherapy via portal infusion proved to be feasible in a multicenter setting. Follow-up will be continued, in order to provide definitive information on survival according to randomization.