In recent years, biologic response modifiers, including recombinant cytokines and hematopoietic growth factors, have been used to treat patients with refractory hematologic malignancies and solid tumors, as well as chemotherapy-associated myelosuppression and thrombocytopenia and treatment- and/or malignancy-related anemia. Various cytokines appear to be effective in patients with hematologic malignancies, but long-term and durable responses in the salvage setting are rare. In patients with solid tumors, such as renal cell carcinoma, malignant melanoma, and colorectal cancer, cytokines may have a limited role in primary therapy but are of little value in salvage therapy. Complications of malignancy and antineoplastic therapy are widely treated with hematopoietic growth factors, like granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor, and more recently the interferons and interleukins have demonstrated a potential role in this setting.