It is studied the existence of periodic oscillations of a one-dimensional c
hain of particles periodically perturbed and with nearest-neighbor interact
ion between particles, It turns out that the behavior of the system is diff
erent if the number of particles is finite or infinite. In both cases, nece
ssary and sufficient conditions for existence of periodic solutions are obt
ained over the mean values of the external forces by using a priori bounds,
topological degree and limiting arguments.