  We present the full next-to-next-to-leading order (NNLO) coefficient
functions for the polarized cross section $d\Delta \sigma/dQ$ for the Drell-Yan
process $p + p\to l^+l^- + 'X'$. Here $'X'$ denotes any inclusive hadronic
state and $Q$ represents the invariant mass of the lepton pair. All QCD
partonic subprocesses have been included provided the lepton pair is created by
a virtual photon, which is a valid approximation for $Q<50$ GeV. Unlike the
differential distribution w.r.t. transverse momentum the dominant subprocess
for the integrated cross section is given by $q+\bar q \to \gamma^* + 'X'$ and
its higher order corrections so that massive lepton pair production provides us
with an excellent tool to measure the polarized anti-quark densities. Our
calculations are carried out using the method of $n$-dimensional regularization
by making a special choice for the $\gamma_5$ matrix. We give predictions for
double longitudinal spin asymmetry measurements at the RHIC.
