  We discuss three different cases of hard inclusive spectra in proton-proton
collisions: high $p_T$ single hadron production at $\sqrt{s}\approx$ 20 GeV and
at $\sqrt{s}$ = 62.4 GeV, and direct photon production at $\sqrt{s}$ = 200 GeV;
with regard to their relevance for the search of Quark Gluon Plasma signals in
A+A collisions at SPS and RHIC energies.
