  We derive a closed expression for the finite-temperature conductance of a
Coulomb-blockade quantum dot in the presence of an exchange interaction and a
parallel magnetic field. Parallel-field dependence of Coulomb-blockade peak
position has been used to determine experimentally the ground-state spin of
quantum dots. We find that for a realistic value of the exchange interaction,
the peak motion can be significantly affected at temperatures as low as kT ~
0.1 Delta, with Delta being the mean level spacing in the dot. This temperature
effect can lead to misidentification of the ground-state spin when a level
crossing occurs at low fields. We propose an improved method to determine
unambiguously the ground-state spin. This method takes into account level
crossings and temperature effects at a finite exchange interaction.
