We present a code for the QCD-based description of high-energy collisi
ons between longitudinally polarized nucleons. This code is based on P
YHTIA, a code for the description of unpolarized nucleon-nucleon colli
sions. We implemented the polarized cross sections and introduced pola
rized distribution functions. Polarized proton-proton collisions will
be studied at RHIC (BNL). The implementation of transverse polarizatio
n requires fundamental changes in the structure of the code and was no
t yet done.