Values of the second order hyperpolarizability β have been determined for p-nitroaniline (PNA) in solvents of varying polarity using the electric field induced second harmonic generation experimental technique. An observed solvent dependence of β0, the second order hyperpolarizability extrapolated to zero-frequency, is correlated with the solvent-induced shift of the PNA charge transfer absorption maximum λmax. The correlation is similar to the correlation between λmax and β0 observed in donor/acceptor p-substituted benzenes with different substituents. Both dependences can be understood within the framework of a simple four level Hückel model. © 1992.