The second-order nonlinear optical properties of maghemite crystallites were experimentally studied in chloroform solution by hyper-Rayleigh scattering. The hyperpolarizability on a per particle basis was found to be extremely large, i.e., on the order of 92 000 10(-30) esu. However, when the hyperpolarizability was calculated on a per volume basis, the nonlinearity agreed well with the macroscopic nonlinearities of typical inorganic crystals. (C) 2003 Elsevier B.V. All rights reserved.