The electro-optical coefficient r(33) and refractive index of films of poly(gamma-benzyl-L-glutamate) and the p-nitro, p-fluoro and p-trifluoromethyl derivatives were determined as a way to assess the non-linear optical behaviour of these organic polymers. The p-fluoro-gamma-benzyl and p-trifluoromethyl-gamma-benzyl ester polymers are new materials synthesized for this study. The electro-optical coefficient r(33) = 5.2 x 10(-2) pm V-1 for the unsubstituted polymer, 13.9 x 10(-2) pm V-1 for the p-nitro polymer, 3.0 x 10(2) pm V-1 for the p-fluoro polymer, and 1.6 x 10(-2) pm V-1 for the p-trifluoromethyl polymer. The refractive indices, at a wavelength of 488 nm, of films of the polymer were determined to be 1.60, 1.61, 1.59, and 1.70, respectively, for the unsubstituted polymer and the p-nitro, p-fluoro, and p-trifluoromethyl derivatives. The frequency dependence of the dielectric constant, from 10 kHz to 4 MHz, for each of the polymer films was also determined. The waveguiding and other properties of each of the polymers were assessed in terms of the polymer structure.