  Charged black holes, both spherically symmetric and rotating, in the low
energy limit of string theory (Einstein-Maxwell-dilaton theory) are compared to
analogous geometries in pure general relativity. We describe various physical
differences and investigate some experiments which can distinguish between the
two theories. In particular we discuss the gyro-magnetic ratios of rotating
black holes and the propagation of light on black hole backgrounds. For the
former we obtain an expression in the Einstein frame (EF) which is different
from the one in the String frame (SF). This (and other results) can be used to
test the stringy nature of matter. For a binary system consisting of a star and
a rotating black hole, we give estimates of the damping of electro-magnetic
radiation coming from the star due to the existence of a scalar component of
gravity.
