We have studied the pretransitional behaviour at the nematic-isotropic transition for two systems by simulating the second-rank Kirkwood g-factor in the isotropic phase using the Monte Carlo technique. The Lebwohl-Lasher model was used for one nematogen while for the other the simple anisotropic intermolecular potential was replaced by a truncated dispersion potential. The simulated g$_2$-factor is found to diverge for both potentials as the nematic-isotropic transition is approached, in accord with the anticipated increase in angular correlations. The divergence in g$_2$ observed for the two anisotropic potentials is compared with experiment and with the predictions of the Landau-de Gennes theory. The best agreement for both theory and experiment is found for g$_2$ simulated with the simple potential.