  We propose an effective action for the eleven-dimensional (bosonic)
Kaluza-Klein monopole solution. The construction of the action requires that
the background fields admit an Abelian isometry group. The corresponding
sigma-model is gauged with respect to this isometry. The gauged sigma-model is
the source for the monopole solution. A direct (double) dimensional reduction
of the action leads to the effective action of a 10-dimensional D-6-brane (IIA
Kaluza-Klein monopole). We also show that the effective action of the
10-dimensional heterotic Kaluza-Klein monopole (which is a truncation of the
IIA monopole action) is T-dual to the effective action of the solitonic
5-brane. We briefly discuss the kappa-symmetric extension of our proposal and
the possible role of gauged sigma-models in connection with the conjectured
M-theory 9-brane.
