The spatial structure of the neurokinin A molecule was studied by the method of theoretical conformational analysis. On the basis of fragmental analysis, stable structures of the neurokinin A molecule under polar conditions were determined. The structures can be described by four families of low-energy conformations having a relatively labile tripeptide at the C-end and a conformationally rigid heptapeptide at the N-end. It was shown that two of these conformations are virtually isoenergetic structures. One of these is an alpha-helical structure and the other forms two beta-turns at the N-terminus, which change to the turn of the alpha-helix at the C-end.