Supersymmetric black holes in N=8 supergravity

We study the embedding of extreme (multi-) dilaton black hole solutions for the values of the parameter a=\sqrt{3},1,1/\sqrt{3},0 in N=4 and N=8 four-dimensional supergravity. For each black hole solution we find different embeddings in N=4 supergravity which have different numbers of unbroken supersymmetries. When embedded in N=8 supergravity, all different embeddings of the same solution have the same number of unbroken supersymmetries. Thus, there is a relation between the value of the parameter a and the number of unbroken supersymmetries in N=8 supergravity, but not in N=4, and the different embeddings must be related by dualities of the N=8 theory which are not dualities of the N=4 theory. The only exception in this scheme is a {\it dyonic} embedding of the a=0 black-hole solution which seems to break all supersymmetries both in the N=4 and in the N=8 theories.