The descriptions of Reissner-Nordstrom and Kerr-Newman dilatonic black hole
s in the Einstein frame are compared to those in the string frame. We descr
ibe various physical measurements in the two frames and show which experime
nts can distinguish between the two frames. In particular we discuss the gy
romagnetic ratios of black holes, the decay law via Hawking radiation and t
he propagation of light on black hole backgrounds.