In this paper we consider the problem of finding periodic solutions of certain Euler-Lagrange equations which include, among others, equations involving the p-Laplace operator and, more generally, the pp, qq-Laplace operator. We employ the direct method of the calculus of variations in the framework of anisotropic Orlicz-Sobolev spaces. These spaces appear to be useful in formulating a unified theory of existence of solutions for such a problem. * SECyT-UNRC, FCEyN-UNLPam and CONICET † SECyT-UNRC, FCEyN-UNLPam and UNSL 2010 AMS Subject Classification. Primary: 34C25. Secondary: 34B15.