Cholesteryl oleate and cholesteryl oleyl carbonate have been studied in the vicinity of the isotropic-blue phase transition by nonlinear dielectric effect (NDE), electro-optical Kerr effect (EKE) and optical rotation (OR) methods. The electrically induced pretransitional effects follow the classical 1/( T-T*) behaviour, the OR reveals more complex behaviour. The noncritical background due to contributions from individual molecules, is observed by the NDE method. The electric permittivity anisotropies of the perfectly ordered phase are determined from the ratio of the NDE to EKE amplitudes. Some procedures which yield the accurate determination of the Kerr constant in chiral systems are discussed.