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The importance of including electron correlation effects in the determination of the equilibrium structure and hyperpolarizabilities of p-nitroaniline is investigated. Second-order perturbation theory gives static hyperpo-larizabilities which are 88% to 100% larger than those obtained without electron correlation. These values are scaled by a self-consistent field frequency-dependent contribution for comparison with experimental measurements. Despite the large increase in ß (-2;,) from electron correlation, the theoretical result is still 3 times smaller than the experimental value obtained in solution. This difference is discussed. The finite field perturbation approach for calculating hyperpolarizabilities is discussed, and we outline a generalization of a previous method based on the solution of simultaneous equations.