  Recently determined next-to-leading order sets of polarized parton
distributions are used to study large-p_T $\vec{p}\vec{p}\rightarrow \gamma+X$
at $\sqrt{s}=38, 100 and 500 GeV$. Certain conversion terms, necessary to use
the above sets, are determined. It is concluded that, to distinguish between
the above sets, planned RHIC experiments should be successful, in particular at
c.m. photon pseudorapidity $\simeq 1$, and that a proposed HERA-$\vec{N}$ fixed
target experiment should have rather large accuracy at relatively large $x_T
(=2p_T/\sqrt{s})$.
