GATA-2 is a member of a family of transcription factors which bind a common DNA sequence motif (WGA-TAR) through an evolutionarily conserved zinc finger domain. An essential role for GATA-2 in the development of hematopoietic stem cells has recently been shown in gene targeting experiments in mice. Here we show that GATA-2 exists in hematopoietic progenitor cells as a phosphoprotein. Stimulation of progenitors with interleukin-3 (IL-3) results in enhanced phosphorylation of GATA-2 which occurs within 5 min. IL-3 is known to signal in part through mitogen-activated protein (MAP) kinase, and evidence for MAP kinase signaling in the control of GATA-2 phosphorylation was obtained by genetically manipulating the MAP kinase pathway in COS cells using either constitutively activating or interfering mutants of MAP kinase kinase. Furthermore, using an interfering mutant of MAP kinase kinase, we directly demonstrated a critical role for the MAP kinase pathway in the IL-3-dependent phosphorylation of GATA-2 in hematopoietic progenitor cells. Finally, in vitro phosphorylation experiments using recombinant GATA-2 raise the possibility that MAP kinase itself may phosphorylate GATA-2. Our results provide evidence for phosphorylation via the MAP kinase pathway constituting a cytoplasmic link between GATA-2 and growth factor receptors and are consistent with the hypothesis that GATA-2 is involved in the growth factor responsiveness and proliferation control of hematopoietic progenitor cells.