Valeri V. Dvoeglazov (EFUAZ) The Second-Order Equation from the (1/2,0)+(0,1/2) Representation of the Poincare Group (15K, ReVTeX) ABSTRACT. On the basis of the first principles we derive the Barut-Wilson-Fushchich second-order equation in the (1/2,0)+(0,1/2) representation. Then we discuss the possibility of the description of various mass and spin states in such a framework.