A short review of literature and the authors' experimental results for the pretransitional behavior in the isotropic phase of nematogens is given. The paper also presents new results of non-linear dielectric effect and dielectric
permittivity measurements in the broad temperature range. Results obtained show significant advantages of non-linear dielectric effect and dielectric permittivity for studying pretransitional properties in liquid crystalline
materials. The paper contains a comprehensive comparison of the experiment with predictions of the mean-field model and the fluid-like description. The presented analysis strongly supports the image of the isotropic phase as
a complex liquid resulting from vicinity of the fluid-like, "nematic-isotropic", critical point