  Our aim is to test a model recently presented, motivated by the reported
$R_b$ and $R_c$ ``crisis", which contains extra vector fermions. We suggest an
alternative indirect test of the possible existence of new heavy quark flavours
at the LEP2 collider, which turns out to give the clearest signal. We calculate
$q\bar{q}$ cross sections within this framework, including one loop
corrections, and find measurable differences compared to the Standard Model
predictions.
