We evaluated the role of low-dose alpha-2b interferon, added to chemotherapy, for advanced colorectal cancer; we randomized patients, to either a combination chemotherapy of 5-fluorouracil (5-FU) and high-dose folinic acid (HDFA) or the same regimen plus interferon. Between January 1990 and March 1992, 100 untreated patients (PTS) with advanced colorectal cancer, 53 men and 47 women, with an ECOG performance status (PS) of < or = 3, were randomized to either HDFA 200 mg/m2 iv bolus and 5FU 370 mg/m2 in 15-min iv infusion days 1-5 every 4 weeks (arm A), or the same chemotherapy plus IFN 3 x 10(6) IU subcutaneously three times a week in chemotherapy intervals (arm B). A total of 97 PTS are evaluable for response, toxicity, and survival; 3 PTS are not evaluable in arm B for major protocol violations. PTS characteristics were well balanced in both arms for age (median, 64 years), disease-free survival, and disease site. ECOG PS was 0 in 28% of PTS in arm A and in 13% in arm B. Response rates were as follows: arm A, 40%; and arm B, 23%. Median time to failure was as follows: 10.2 months arm A versus 9 months arm B. Median survival was as follows: 13.3 months arm A versus 10.9 months arm B. Grade 3 haematological toxicity was 9% of PTS in both arms. Gastrointestinal toxicity was as follows: 17% arm A versus 22% arm B. The cost of drugs expressed per m2/month was $60 in arm A and $390 in arm B. The results show that IFN at the schedule and doses employed adds no benefit to the combination of 5FU/HDFA.