Inverse gas chromatography (IGC) was used to study:the thermal transitions in an organic; liquid-crystalline polyester. A crystal-to-nematic and a nematic-to-isotropic transition were detected, as was a lower temperature transition, presumably a crystal-to-crystal transition. The probe molecules used were nonsolvents of the polyester, which was insoluble in normal organic solvents. The IGC retention diagram, or a plot of the apparent weight fraction activity coefficient vs inverse temperature, could be used for the determination of the transition temperature.