We consider the Bekenstein-Hawking entropy-area formula in four dimensional
extended ungauged supergravity and its electric-magnetic duality property.
Symmetries of both "large" and "small" extremal black holes are considered, as
well as the ADM mass formula for N=4 and N=8 supergravity, preserving different
fraction of supersymmetry. The interplay between BPS conditions and duality
properties is an important aspect of this investigation.Comment: 45 pages, typos corrected, references adde
