Mononuclear cells generate a variety of hormone-like proteins termed growth factors that are instrumental in the evolution and resolution of inflammatory reactions. Many of these growth regulatory molecules have multifunctional properties. For example, the mononuclear cell-derived growth factors, plateletderived growth factor (PDGF), and transforming growth factor beta (TGF-P), are potent leukocyte chemoattractants. In addition, TGF-8, a product of platelets, T lymphocytes, and monocytes, appears to induce the transcription of other monocytederived growth hormone genes. In this regard, picomolar concentrations of TGF-P stimulate peripheral blood monocytes to transcribe the genes for PDGF (c-sis), basic fibroblast growth factor (FGF), interleukin 1 (IL-l), and tumor necrosis factor (TNF). Furthermore, levels of mRNA for TGF-P, which is constitutively expressed in resting monocytes, are also increased by exogenous TGF-0. Each of these monocyte products exhibits a plethora of biological activities on other cell types. T lymphocytes, in response to antigen, contribute to this network by secreting growth factors and lymphokines that regulate monocyte growth factor production.