Cytokines play key roles in the control of hemopoiesis and immunity. As they become available in increasing quantities and purity through improved recombinant technology, cytokines hold great clinical promise. This article focuses on recent clinical experience with a wide variety of cytokines. For example, newer uses of recombinant human erythropoietin include treatment of anemia of prematurity, AIDS, and some hemoglobinopathies. The myeloid-stimulating factors have established a niche in the treatment of chemotherapy-induced neutropenias and as an adjunct to bone marrow transplantation. Combinations of cytokines that act at different levels of hemopoietic proliferation are being evaluated for the treatment of other causes of neutropenia and thrombocytopenia and also as biologic response modifiers.