The present invention relates to a liquid-crystalline medium based on a mixture of polar compounds of positive or negative dielectric anisotropy which is characterised in that it comprises one or more compounds of the general formula I in which R1 and R2 are each, independently of one another, identically or differently, H, an alkyl radical having from 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, where, in addition, one or more CH2 groups in these radicals may each, independently of one another, be replaced by —O—, —S—, —CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another, to the use thereof for electro-optical purposes, and to electro-optical display devices which contain this medium.