Platelet-activating factor. A putative mediator in central nervous system injury? Platelet-activating factor (1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine) is a potent lipid autacoid produced by many cell types. Platelet-activating factor is produced by cerebellar granule cells in culture and has been extracted from brain tissue. Multiple platelet-activating factor receptors have been demonstrated in brain tissue. Activation of platelet-activating factor receptors in transformed neuronal cell lines involved increases in intracellular calcium. Platelet-activating factor has potent actions on cerebral vessels and cerebral metabolism when administered in vivo, but may not have direct effects on brain microvessels. Excessive platelet-activating factor production in pathological states of the nervous system such as neurotrauma and stroke has been shown in only a few models (e.g., spinal cord ischemia and reperfusion or focal repercussion brain injury). In multiple studies using highly specific and potent platelet-activating factor antagonists, reversal or prevention of key consequences of brain injury such as hypoperfusion following ischemia, reperfusion and edema, inflammatory cell accumulation, neurologic/motor deficits, and neuronal salvage were demonstrated. This review provides and analyzes evidence in support of the role that platelet-activating factor might have in modulation of brain function and pathophysiological processes in brain ischemia and trauma. 