Mammalian tachykinins are traditionally viewed as neuropeptides. This review describes the mammalian tachykinins and evidence for expression of these peptides by non-neuronal cells. Tachykinin expression is defined as evidence for gene transcription, peptide production, or peptide secretion. Since the functions of mammalian tachykinins have been amply reviewed, the biological roles of these peptides will be noted briefly, with emphasis on immune cell action. Of particular interest is the predicted existence and non-neuronal expression of new mammalian tachykinins - hemokinin 1, the endokinins and C14TKL-1. Synthetic forms of these peptides have high affinity for the NK₁ receptor, the protein traditionally associated with substance P binding. By acting on the same "substance P" receptor, these tachykinins have the potential for promoting similar post-receptor functions. The structure and action of representative non-mammalian tachykinins acting on mammals are also presented. These peptides, of interest in their own right, also appear to exhibit selectivity for the NK₁ receptor. They strengthen the notion that multiple ligands may be capable of binding to one receptor, NK₁, effecting similar cellular responses.