Polymorphonuclear neutrophils (PMNs) are usually thought of as the leukocyte population involved in acute inflammatory responses, acting as a first line of defense against invading microorganisms. These terminally differentiated cells are generally not thought of as an important source of de novo synthesis of polypeptide mediators. Recent progress has shown, however, that PMNs are able to synthesize cytokines in response to a variety of inflammatory stimuli and during certain pathological conditions. The expression profiles of PMN-derived cytokines are similar with those of monocytes/macrophages, major professional phagocytes. Like monocytes, PMNs are able to secrete proinflammatory cytokines [e.g., tumor necrosis factor (TNF)-α and interleukin (IL)-1β], both CC and CXC chemokines [e.g., IL-8, interferoninducible protein 10 (IP-10) and macrophage inflammatory protein (MIP)-1α], and angiogenic factors [e.g., vascular endothelial growth factor (VEGF)]. The secretion of cytokines by activated PMNs is regulated by immunoregulatory cytokines such as interferon (IFN)-γ, IL-4, IL-10 and IL-13. In addition to acute inflammatory responses, PMNs and PMN-derived cytokines appear to be involved in the pathogenesis of such chronic inflammatory disorders as rheumatoid arthritis, inflammatory bowel diseases and mycobacterial infections. Conceivably, these findings place PMNs at a pivotal position where they regulate and orchestrate not only acute inflammatory responses but also chronic inflammation and immune regulation. As such, inhibition of PMN-derived cytokines is viewed as a potentially useful strategy for therapeutic immunointervention.