  We analyze the Coulomb phase of theories of $N=2$ SQCD with $SU(N_c)$ gauge
groups which are conjectured to have exact electric-magnetic duality. We
discuss the duality transformation of the particle spectrum, emphasizing the
differences between the general case and the $SU(2)$ case. Some difficulties
associated with the definition of the duality transformation for a general
gauge group are discussed. We compute the classical monopole spectrum of these
theories, and when it is possible we use it to check the consistency of the
duality. Generally these theories may have phase transitions between strong and
weak coupling, which prevent the semi-classical computation from being useful
for checking the duality.
