Subcutaneous administration of low doses of recombinant interleukin-2 (IL-2) and interferon-alpha (IFN-alpha) on an out-patient basis has been reported not to significantly compromise the response frequency compared to intravenous IL-2 in patients with renal cell carcinoma and melanoma. As part of an ongoing program to develop a biotherapeutic concept in patients with colorectal carcinoma (CRC) we studied the clinical effects of such a regimen in 15 patients with metastatic CRC. The daily dose of IL-2 varied between 4.8-14.4 x 10(6) U/m2 and of IFN-alpha between 3-6 x 10(6) U/m2. The cycle length was 6 weeks. The course was repeated every 8 weeks until disease progression. Maximum 4 cycles were administered. Maintenance therapy was given to responding patients once a week every month. No patient showed a major response (CR or PR). Six patients had a stable disease ranging from 3 months to 18 months with a median duration time of 5 months. The median survival of all patients was 13 months. The main adverse reactions were fever, chills, anorexia and shortness of breath. No treatment related deaths occurred. 6/14 patients developed abnormal concentration of serum levels of thyroid hormones. It is concluded that the present treatment schedule using IL-2 and IFN-alpha in advanced CRC seemed not to be of clinical benefit.