The tachykinins are a group of related peptides that are mainly synthesized in the central and peripheral nervous system, but are also present in peripheral non-neuronal cells. In humans, substance P (SP) is the most extensively studied tachykinin and is present, along with the NK-1 receptor, in several inflammatory and immune cells. The release of SP under the appropriate stimulus may act as a paracrine or autocrine signal that may help to initiate and/or propagate inflammation. In the present study we have determined the expression pattern of NKB and HK-1 mRNA in human lymphocytes, monocytes, neutrophils and eosinophils. In addition, we have detected for the first time the presence of NKB protein in these cellular types. These findings reinforce the suggestion that tachykinins play a central role in the pathophysiology of the inflammatory process.