Timelike and spacelike hard exclusive reactions

We show to next-to-leading order accuracy in the strong coupling alpha(s) how the collinear factorization properties of QCD in the generalized Bjorken regime relate exclusive amplitudes for spacelike and timelike hadronic processes. This yields simple space-to-timelike relations linking the amplitudes for electroproduction of a photon or meson to those for photo- or mesoproduction of a lepton pair. These relations constitute a new test of the relevance of leading twist analyses of experimental data.