Discovered in 1983, the decapeptide neurokinin A has been shown to occur in several peripheral organs and to exert a variety of biological effects. In this article, we review the most sensitive and selective in vivo and in vitro tests which have been used in various laboratories to evaluate naturally occurring or synthetic neurokinin A. A comparison of the effects of neurokinin A and those of its mammalian homologues, substance P and neurokinin B as well as those of tachykinins and related peptides is presented in the frame of a study directed toward characterization of neurokinin receptors. Indeed, neurokinin A has been shown to be particularly active on a neurokinin receptor subtype, the NK-2. Structure-activity studies performed with neurokinin A and its fragments as well as with several analogues of both the decapeptide and the heptapeptide NKA(4-10) have brought to the identification of the minimum structure required for activation of NK-2 receptors. Selective agonists for this receptor have been identified, in particular [Nle10]-NKA(4-10) and [beta-Ala8]-NKA(4-10).