Cytokines are known to influence hematopoietic precursor cell survival. Apoptosis (a programmed cell death pathway) has been identified as the key factor limiting hematopoietic precursor cell survival and cytokines have been demonstrated to induce or prevent apoptosis in a variety of hematopoietic precursor cell populations. Whether a specific cytokine inhibits or suppresses apoptosis depends on cytokine-mediated modulation of target cell cytokine receptors, cell death regulator genes such as bcl-2 family members, Fas receptor, and other pathways. Finally, the intracellular pathways of cytokine receptor-mediated control of apoptosis have begun to be unraveled, implicating specific intracellular receptor domains and protein kinases in the regulation of apoptosis and hematopoietic precursor cell survival.