Abstract. We have calculated the one-loop supersymmetric corrections to the parton scattering subprocesses and , including form-factor corrections and box diagrams with internal squarks and gluinos of arbitrary mass. In general, these exhibit cusps at the corresponding direct-channel sparticle thresholds. We use these calculations to make numerical estimates of the possible threshold effects at the Fermilab Tevatron collider and at the LHC, which depend on the rapidity range selected, but can be as large as a few percent. These effects are diluted in the integrated large- cross section, where they are negative.