  In the supersymmetric extension of the Standard Model we derive the two-loop
QCD corrections to the scalar quark contributions to the electroweak precision
observables entering via the rho parameter. A very compact expression is
derived for the gluon-exchange contribution. The complete analytic result for
the gluino-exchange contribution is very lengthy; we give expressions for
several limiting cases that were derived from the general result. The two-loop
corrections, generally of the order of 10 to 30% of the one-loop contributions,
canbe very significant. Contrary to the Standard Model case, where the QCD
corrections are negative and screen the one-loop value, the corresponding
corrections in the supersymmetric case are in general positive, therefore
increasing the sensitivity in the search for scalar quarks through their
virtual effects in high-precision electroweak observables.
