Details of the thermal behaviour of the following liquid-crystalline ‘backbone’ copolyester are reported: — [OCC6O]0.6+[OOCC6H4OCH2CH2OC2H4COOCH2CH2]0.4? Between 218° and 337°C, observations using a polarizing microscope indicate the formation of a birefringent melt that exhibits a Schlieren texture. From the observation of disclinations of strength , the mesophase can be identified as a nematic phase. The isobaric phase diagram of mixtures of copolyester and N,N′-di-(ρ-methoxy benzylidene)-α,α′-bi-ρ-toluidine and X-ray diffraction patterns provide definite proof as to the nematic structure of the birefringent melt. Addition of a chiral compound to the copolyester in the nematic state causes the formation of the typical textures of cholesterics. The temperature dependence of the order parameter has been determined from FTi.r. polarized spectra. At high temperature S is found to be 0.3. Such a result confirms the recent theory of Ronca and Yoon: the isotropic-nematic transition of semiflexible polymers does not entail a very high degree of order in the resultant nematic phase.