Extensive efforts since 1931, on the structural determination of the mammalian tachykinin SP by NMR, CD and IR have turned out to be inconclusive. Studies are now being concentrated on the structural properties and characteristics of various NK receptors (NK1, NK2 and NK3) with the help of genetics, cloning, receptor engineering, mutagenesis and modeling. This knowledge is now being fruitfully used in the development of non-peptide NK1 receptor antagonists that essentially block the pharmacological effects of SP. It is now being realized that the simultaneous blockade of two or more receptors gives promising results in emesis, depression and pulmonary obstructive diseases. In addition to the synthetic compounds, the discovery of antagonists from natural origin has added a great value to this field. In this review we have made an attempt to present the structural characteristics of SP, its analogs and antagonists, the structural characteristics of the NK receptor, and structure activity relationships that have helped to improve the therapeutic utilities of SP antagonists.