  We treat the horizons of charged, dilaton black extended objects as quantum
mechanical objects. We show that the S matrix for such an object can be written
in terms of a p-brane-like action. The requirements of unitarity of the S
matrix and positivity of the p-brane tension equivalent severely restrict the
number of space-time dimensions and the allowed values of the dilaton parameter
a. Generally, black objects transform at the extremal limit into p-branes.
