  We study the bifurcation values of real polynomial maps $f: \bR^{2n} \to
\bR^2$ which reflect the lack of asymptotic regularity at infinity. We
formulate real counterparts of some structure results which have been
previously proved in case of complex polynomials by Kushnirenko, N\'emethi and
Zaharia and other authors, emphasizing the typical real phenomena that occur.
