  We consider absolutely irreducible polynomials $f \in Z[x,y]$ with
$\deg_x(f)=m$, $\deg_y(f)=n$ and height $H$. We show that for any prime $p$
with $p>c_{mn} H^{2mn+n-1}$ the reduction $f \bmod p$ is also absolutely
irreducible. Furthermore if the Bouniakowsky conjecture is true we show that
there are infinitely many absolutely irreducible polynomials $f \in Z[x,y]$
which are reducible mod $p$ where $p$ is a prime with $p>H^{2m}$.
