  The hadroproduction of lepton pairs with mass Q and finite transverse
momentum Q_T is described in perturbative QCD by the same partonic subprocesses
as prompt photon production. We demonstrate that, like prompt photon
production, lepton pair production is dominated by quark-gluon scattering in
the region Q_T>Q/2. This feature leads to sensitivity to the gluon density in
kinematical regimes accessible in collider and fixed target experiments, and it
provides a new independent method for constraining the gluon density.
