A phase II study on recombinant human leukocyte A interferon (rIFN-alpha A) was carried out in 30 patients with urogenital cancers. Each patient received rIFN-alpha A by i.m. injection every day for at least 4 weeks. The initial daily dose was 3 X 10(6) U, being escalated at intervals of 3 days or more up to 50 X 10(6) U. The results are summarized as follows: In aged patients, the daily dose appropriate for everyday i.m. injection was considered to be 9 X 10(6) U or below, judging from the adverse reactions observed. According to Koyama and Saito's response criteria, partial response (PR) and minor response (MR) were obtained, respectively, in 3 and 1 out of 12 patients with renal cell carcinoma, while PR was seen in 1 out of 9 with urothelial cancer. No response was observed in patients with testicular cancer and in those with prostatic cancer. Various kinds of adverse reactions were recognized and each patient showed one reaction or more. Fever, fatigue, leukopenia, anemia, thrombocytopenia and elevation of GOT and GPT were observed relatively frequently. Among these, fatigue and thrombocytopenia were regarded as dose limiting factors.