A clinical trial using human lymphoblastoid interferon (HLBI) was done on patients with advanced renal cell carcinoma to compare the efficacy of monotherapy with that of combined administration with a 5-fluorouracil (FU) agent. A total of 24 patients with definitely diagnosed advanced renal cell carcinoma were enrolled in either of the HLBI treatments. Principally, the daily intramuscular injection of 3 million units of HLBI was done for 4 consecutive days and thereafter followed by twice of weekly injections. The combined agent used in the present study was 300 or 600 mg of 5-fluorouracil agent given orally. The efficacy of HLBI was evaluated according to direct assessment standard of chemotherapy to a solid tumor expelled by the committee of Japanese health and welfare ministry. Of 11 patients who received monotherapy, 3 had a partial response rate of 27.3 percent. While only one of 13 patients having received combined HLBI administration with oral 5-FU tablets showed a partial response with a response rate of 7.7 percent. A total of 4 patients partially responded to either HLBI treatment with a subsequent response of 16.7 percent. Partial response implied reduction of lung metastatic foci in 3 patients and primary lesion in one patient. There was observed untoward fever-up in all patients with HLBI injections which was relieved with acquired tachyphylaxis owing to repeated injections. Otherwise minimal adverse effects were temporary elevation of liver transaminase in 4 and leucopenia in 2 patients during the HLBI treatment both of which eventually returned to the normal level without discontinuation of HLBI therapy.(ABSTRACT TRUNCATED AT 250 WORDS)