  We report the enhancement of the optical second harmonic signal in
non-centrosymmetric semiconductor CdS quantum dots, when they are placed in
close contact with isolated silver nanoparticles. The intensity enhancement is
about 1000. We also show that the enhancement increases when the incoming laser
frequency $\omega$ is tuned toward the spectral position of the silver plasmon
at $2\omega$, proving that the silver nanoparticle modifies the nonlinear
emission.
