  Using standard field theory techniques we compute perturbative and instanton
contributions to the Coulomb branch of three-dimensional supersymmetric QCD
with N=2 and N=4 supersymmetry and gauge group SU(2). For the N=4 theory with
one massless flavor, we confirm the proposal of Seiberg and Witten that the
Coulomb branch is the double-cover of the centered moduli space of two BPS
monopoles constructed by Atiyah and Hitchin. Introducing a hypermultiplet mass
term, we show that the asymptotic metric on the Coulomb branch coincides with
the metric on Dancer's deformation of the monopole moduli space. For the N=2
theory with $N_f$ flavors, we compute the one-loop corrections to the metric
and complex structure on the Coulomb branch. We then determine the
superpotential including one-loop effects around the instanton background.
These calculations provide an explicit check of several results previously
obtained by symmetry and holomorphy arguments.
