The intravenous immunotherapy with high-dose interleukin-2 (IL-2) would constitute one of the most effective treatments of metastatic renal cell carcinoma (RCC). More recently, IL-2 subcutaneous therapy has also appeared active, either alone or in association with interferon, with results comparable to those found with the intravenous route of injection, but with a lower toxicity. On this basis, we have designed a protocol of treatment with low-dose IL-2 alone given subcutaneously as a first or a second line therapy in metastatic RCC. The study included 60 consecutive patients (pts) (M/F: 39/21, median age 56 years, range 26/74). IL-2 was given at a dose of 3 millions IU twice/day for 5 days/week, for 6 weeks, corresponding to one cycle. In non progressed pts a second cycle was repeated after a 28-day rest period. Dominant metastasis sites were, as follows: soft tissues: 8; bone: 11; lung: 29; liver: 3; liver plus lung: 7; adrenal: 2. The minimum follow-up was 18 months and the median follow-up was 34 months (range 18-48). A complete response (CR) was achieved in 2/60 (3%) pts. A partial response (PR) was obtained in 15/60 (25%). Therefore, tumor objective rate (CR + PR) was 17/60 (28%). The median duration of response was 13 months (4-33).(ABSTRACT TRUNCATED AT 250 WORDS)