Keywords--Pala is-Smale condition, Critical point theory, Hamiltonian systems, Perturbation from symmetry, Multiple periodic solutions. 1. I N T R O D U C T I O N In this paper, in the spirit of [1], we want to investigate the effect of perturbing the S l symmet ry of a general class of Hamiltonian systems. Studied around 1980 by Bahri and Berestycki in [2], the problem of finding multiple peri...