Spincoated thin films of a chiral poly(3-alkylthiophene) were investigated by second-harmonic generation. Based on a study of the polarization dependence of the second-harmonic signal, we were able to show that significant magnetic-dipole contributions are present in the nonlinearity of the films, in addition to the usual electric-dipole contributions. (C) 2005 Elsevier B.V. All rights reserved.