Abstract: The invention relates to a liquid-crystalline medium having a nematic phase comprising one or more compounds of formula X wherein the parameters have the meaning given in the text, to the use thereof in an electro-optical display, particularly in an active-matrix display based on the IPS or FFS effect, to displays of this type which contain a liquid-crystalline medium of this type and to the use of the compounds of formula X for improvement of the transmission and/or response times of a liquid-crystalline medium which comprises one or more additional mesogenic compounds, as well as to certain compounds of formula X, as specified in the text.