With the availability of recombinant interleukin-2, multiple trials of cancer therapy with this lymphokine have been undertaken. The most successful trials have documented complete or partial responses in patients with metastatic renal cell carcinoma and melanoma. However, IL-2 therapy has been ineffective in the treatment of breast cancer, colon cancer, and lymphoma. The therapy is not innocuous. All patients exhibit a marked lymphocytosis, eosinophilia, fluid retention, fever, and decrease in peripheral vascular resistance, effects similar to those of septic shock.