  We revisit the moduli space approximation to the quantum mechanics of
monopoles in N=4 supersymmetric Yang-Mills-Higgs theory with maximal symmetry
breaking. Starting with the observation that the set of fermionic zero-modes in
N=4 supersymmetric Yang-Mills-Higgs theory can be viewed as two copies of the
set of fermionic zero-modes in the N=2 version, we build a model to describe
the quantum mechanics of N=4 supersymmetric monopoles, based on our previous
paper [1] on the N=2 case, in which this doubling of fermionic zero-modes is
manifest throughout. Our final picture extends the familiar result that quantum
states are described by differential forms on the moduli space and that the
Hamiltonian operator is the Laplacian acting on forms. In particular, we derive
a general expression for the total angular momentum operator on the moduli
space which differs from the naive candidate by the adjoint action of the
complex structures. We also express all the supercharges in terms of (twisted)
Dolbeault operators and illustrate our results by discussing, in some detail,
the N=4 supersymmetric quantum dynamics of monopoles in a theory with gauge
group SU(3) broken to U(1) x U(1).
