  We establish a characterization of dualizing modules among semidualizing
modules. Let R be a finite dimensional commutative Noetherian ring with
identity and C a semidualizing R-module. We show that C is a dualizing R-module
if and only if Tor_i^R(E,E') is C- injective for all C-injective R-modules E
and E' and all i\geq 0.
