  We outline a proof of the stability of a massless neutral scalar field $\psi$
in the background of a wide class of four dimensional asymptotically flat
rotating and ``electrically charged'' solutions of supergravity, and the low
energy limit of string theory, known as STU metrics. Despite their complexity,
we find it possible to circumvent the difficulties presented by the existence
of ergo-regions and the related phenomenon of super-radiance in the original
metrics by following a strategy due to Whiting, and passing to an auxiliary
metric admitting an everywhere lightlike Killing field and constructing a
scalar field $\Psi$ (related to a possible unstable mode $\psi$ by a non-local
transformation) which satisfies the massless wave equation with respect to the
auxiliary metric. By contrast with the case for $\psi$, the associated energy
density of $\Psi$ is not only conserved but is also non-negative.
