Abstract. We consider the two parametric
family of perturbed Lienard equations
$$\ddot{x}+f(x)\dot{x}+g(x,\dot{x},t,\varepsilon)=0.\qquad\qquad\qquad\qquad
(*)$$ Here $\varepsilon$ is a parameter and $f(x),\
g(x,\dot{x},t,\varepsilon)$ are polynomials with respect to x, y and C^{r}, r > 1 with respect to t. Equation (*)is an effect of
nonlinear forcing on the Lienard equation. Our aim is to show the
persistence of periodic solutions of Lienard equation (if there is any)
under perturbations. Therefore first we find some condition under which the
Lienard equation has at least one periodic orbit, and then we investigate
the persistence of the periodic orbit under perturbation (equation (*)).
The techniques that we use are techniques of Chicone and Melnikov
