Cu-II- and Zn-II-based donor-acceptor porphyrins have been examined for second-order nonlinear optics using the hyper-Rayleigh scattering technique at 1064 nm. Introduction of the metal ions enhances the first hyperpolarizability (beta) of the free-base donor-acceptor porphyrins significantly. The open shell Cu-II (d(9)) has a greater influence on beta of these porphyrin systems than the closed shell Zn-II (d(10)). The high beta values in the Zn-II porphyrins are understood in terms of the change in dipole moments upon excitation within the context of the two-state model as well as two-photon resonance enhancement. In Cu-II porphyrin complexes a large number of excited states seem to contribute to beta with, perhaps, a little contribution from two-photon resonance at the excitation wavelength.