A total of 21 untreated patients (5 males, 16 females; median age, 55 years; range, 28-72) with advanced measurable colorectal carcinoma were treated with an association of 5-fluorouracil (1000 mg/weekly) and alpha-2 interferon (three times a week s.c.: 6 x 10(6) U in the 1st month, 9 x 10(6) U in the 2nd month, 12 x 10(6) U in the 3rd month and then 18 x 10(6) U) until maximum response or progression of disease. Sites of disease involved liver in 10 patients, lung in 6, supraclavicular lymph nodes in 3, skin in 1, abdomen in 4, and vagina in 1 patient. Nine responses (42.8%) were documented (4 complete and 5 partial) with metastases confined to the liver, lung, nodes and skin. Median duration of response was 11 months (range, 4-17+) and median survival was 10 months (range, 2-17+). Side effects (fever, flu-like syndrome and leukopenia) required a dose reduction of 5-fluorouracil in 8 patients and interferon in 2 patients.