  We calculate the angular distribution of the lepton produced in the Drell-Yan
reaction taking into account pion bound state effects. We work in the kinematic
region where one of the pion constituents goes far off-shell, which allows us
to treat the bound state problem perturbatively. We show that the angular
distribution is very sensitive to the shape of the pion distribution amplitude.
The model we discuss fits the data if we choose a two-humped pion distribution
amplitude suggested by QCD sum rules.
