We prove existence results for solutions of periodic boundary value problems concerning the $n$ th-order differential equation
with $p$ -Laplacian $[\phi (x^{(n-1)}(t))]' = f(t, x(t), x'(t), \dotsc,\linebreak x^{(n-1)}(t))$ and the boundary value conditions $x^{(i)}(0)\!=\! x^{(i)}(T)$ , $i= 0, \dotsc, n-1$ . Our method is based upon the coincidence degree theory of Mawhin. It is interesting that $f$ may be a polynomial and the degree of some variables among $x_0, x_1, \dotsc, x_{n-1}$ in the function $f(t, x_0, x_1, \dotsc, x_{n-1})$ is allowed to be greater than $1$ .