  It is observed that the three-dimensional BTZ black hole is a supersymmetric
solution of the low-energy field equations of heterotic string theory
compactified on an Einstein space. The solution involves a non-zero dilaton and
NS-NS H-field. The entropy of the extreme black hole can then be computed using
string theory and the asymptotic properties of anti-de Sitter space, without
recourse to a D-brane analysis. This provides an explicit example of a black
hole whose entropy can be computed using fundamental string theory, as
advocated by Susskind.
