It is known that interleukin-2 (IL-2) plays a fundamental role in the generation of immune cells capable of mediating tumor regression. Since IL-2 may be often reduced in patients with disseminated cancer, a pilot study was started to evaluate which relation exists between IL-2 levels and survival in metastatic solid neoplasms. The study included 25 patients with metastatic disease (breast cancer: 12; non-small-cell lung cancer: 13). Serum IL-2 levels were measured by radioimmunoassay on venous blood samples collected before the start of chemotherapy. Breast cancer was treated with weekly epirubicin and lung cancer with cisplatin plus etoposide. Low levels of IL-2 were seen in 10/25 patients. Irrespectively of response to therapy and of dominant metastasis sites, the mean survival time was significantly lower in patients with reduced IL-2 concentrations than in those with normal values. These results would suggest that the evidence of low IL-2 levels negatively influences the clinical course of patients with metastatic solid neoplasms.