  Let $F:\Cn \to \Cn$ be a polynomial mapping in Yagzhev's form,i.e.
$$F(x_1,\ld,x_n)=(x_1+H_1(x_1,\ld,x_n),\ld,x_n+H_n(x_1,\ld,x_n)),$$ where $H_i$
are homogenous polynomials of degree 3. In this paper we show that if $\Jac(F)
\in \mathbb{C}^*$ and the Jacobian matrix of $F$ is symmetric, then all the
polynomials $x_i+H_i(x_1,\ld,x_n)$ are irreducible as elements of the ring
$\mathbb{C}[x_1,\ld,x_n]$.
