  We consider the interaction between instantons and anti-instantons in
four-dimensional N=4 super-Yang-Mills theory at large N and large 't Hooft
coupling as described by D-instantons via AdS/CFT duality. We give an estimate
of the strength of the interaction in various regimes. We discuss also the case
of Non-Commutative super Yang-Mills theory where the interaction between
instantons and anti-instantons can be used as a way to probe the locality
properties of the theory in the supergravity picture, without explicit
reference to the definition of local operators.
