  Starting from the self-dual "triplet" of gravitational instanton solutions in
Euclidean gravity, we obtain the corresponding instanton solutions in string
theory by making use of the target space duality symmetry. These dual triplet
solutions can be obtained from the general dual Taub-NUT de Sitter solution
through some limiting procedure as in the pure gravity case. The dual
gravitational instanton solutions obtained here are self-dual for some cases,
with respect to certain isometries, but not always.
