  We prove Griffiths inequalities for the $O(N)$-spin model with inhomogeneous
coupling constants and external magnetic field for any $N\geq 2$. This is
achieved by using a representation of $O(N)$-spins in terms of random paths
that reduces to the random current representation of the Ising model for $N=1$
and an identity that is analogous to the switching lemma for random currents.
