  The vacuum expectation value of an operator carrying magnetic charge is
studied numerically for temperatures above the deconfinement temperature in
SU(2) and SU(3) gauge theory. By analyzing its finite size behaviour, this is
found to be exactly zero in the thermodynamical limit for any T > T_c whenever
the magnetic charge of the operator is different from zero. These results show
that magnetic charge is superselected in the hot phase of quenched QCD.
