We have developed a method for elucidating the spatial contributions of electrons to dynamic second hyperpolarizability, gamma(-omega; omega, omega, -omega), using an analytical expression of the gamma density. The merit of this method is that the dynamic gamma density, whose imaginary part is related to the two-photon absorption (TPA) cross-section, can be calculated easily for each virtual excitation process. This method can also be applied to other dynamic response properties. We present, as an example, an interpretation of the spatial contributions of pi-electrons to Imgamma for trans-stilbene and its donor-disubstituted derivative, i.e... 4, 4'-diamino-trans-stilbene. (C) 2002 Published by Elsevier Science B.V.