Chemotaxis is the process by which leukocytes are directed to sites of inflammation under the influence of a concentration gradient of the soluble chemotactic molecules. Upon encountering a chemotactic molecule, responding leukocytes begin to migrate directionally from regions of low ligand concentrations toward the sites of chemoattractant production that typically possess more substantial levels of soluble chemotactic factors. A number of endogenous proteins have been shown to mediate leukocyte migration, including activated serum components, platelet activating factor (PAF), eucosinoids, cytokines (e.g., IL-1, TNFα, IFN-γ), and neuroendocrine hormones (1). Although many of these factors are believed to play some role in inflammation, their relevance to leukocyte infiltration into inflammatory sites or homing to lymphoid organs has been brought into question.