In this paper we report the dc Kerr constant and the pretransitional temperature of a polar nematic liquid crystal 4-(trans-4'-4'-n-pentylcyclohexy)- benzonitrile (PCH-5). The observed second-order pretransitional temperature T* from our measurements is found to be 1.2 °C below the first-order nematic to isotropic transition temperature. The dependence of the Kerr constant on (T-T*)-1 is found to be in good agreement with the predictions of the Landau-de Gennes model. The highest value of the Kerr constant observed at 632.8 nm is found to be 9.737×10-11 m V-2, corresponding to a temperature of 55.3 °C. © 1992 The American Physical Society.