Measurement of direct photon production at large transverse momentum in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">−</mml:mi></mml:mrow></mml:msup></mml:mrow></mml:math>p,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>p, and<i>pp</i>collisions at 300 GeV/<i>c</i>

Cross sections for inclusive direct photon production in ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p, ${\ensuremath{\pi}}^{+}$p, and pp collisions at 300 GeV/c are measured at transverse momenta ${p}_{T}$ up to 7 GeV/c (${x}_{T}$=0.6). For ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\gamma}X also the rapidity distribution is presented. The cross-section ratio \ensuremath{\sigma}(${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\gamma}X)/\ensuremath{\sigma}(${\ensuremath{\pi}}^{+}$p\ensuremath{\rightarrow}\ensuremath{\gamma}X) is found to be 1 at ${p}_{T}$=4 GeV/c and rises with increasing ${p}_{T}$. This observation signals the occurrence of valence-quark--antiquark annihilation. The results are in good agreement with QCD predictions.