  We discuss the production of pion pairs with a large invariant mass in
hadronic collisions. We present a study based on a perturbative QCD calculation
at full next-to-leading order accuracy, implemented in the computer programme
DIPHOX. We provide a comparison of various predictions with the corresponding
observables measured by the E706 fixed target experiment. Discrepancies between
data and next-to-leading order calculation are carefully analysed. We classify
the theoretical next-to-leading order distributions with respect to their
infra-red sensitivity, and explain which distributions need improvements.
Further, we comment on the energy scale dependences of non pertubative effects.
