We consider the effective nonlinear susceptibility tensord(−2&ohgr;;&ohgr;,&ohgr;)for second harmonic generation in a nonlinear composite medium. We derive a simple expression for this susceptibility in terms of the position-dependent tensord, and three factors that describe the local field enhancement in a corresponding linear medium. The resulting expression can be used to calculate the local-field enhancement ofdin many geometries. In the dilute limit, the general expression reduces to a result previously derived. ©1997 American Institute of Physics.