  The quark <\bar\psi \psi> and gluon <F_{\mu\nu}F^{\mu\nu}> vacuum expectation
values are non-vanishing at low orders in \alpha_s when the perturbative ground
state includes quark and gluon pairs. This offers possibilities of studying the
effects of a non-trivial vacuum using formally exact perturbative methods. The
QCD Feynman rules are modified only for the free, on-shell quark and gluon
propagators at zero four-momentum. Gauge and lorentz invariance is maintained,
while chiral symmetry is spontaneously broken by the ground state.
