A co[poly(ethylene terephthalate)-p-oxybenzoate] containing 80 mole % oxybenzoate units and a copolyester belonging to series of terphenyl derivatives are investigated by DSC and optical microscopy. Their mesophases are identified, by isomorphism with known phases, as nematic and smectic mesophases, respectively. Chiral compounds on addition to these mesophases, cause the formation of the typical textures of cholesterics and twisted smectics C