  We compare `fixed flavor number scheme' (FFNS) and `variable flavor number
scheme' (VFNS) parton model predictions at high energy colliders. Based on our
recent LO- and NLO-FFNS dynamical parton distributions, we generate radiatively
two sets of VFNS parton distributions where also the heavy quark flavors
h=c,b,t are considered as massless partons within the nucleon. By studying the
role of these distributions in the production of heavy particles (h\bar{h},
t\bar{b}, hW^{+-}, Higgs--bosons, etc.) at high energy ep, p\bar{p} and pp
colliders, we show that the VFNS predictions are compatible with the FFNS ones
(to within about 10-20% at LHC, depending on the process) when the invariant
mass of the produced system far exceeds the mass of the participating heavy
quark flavor.
