The synthesis is reported of fifteen three-ring 2,5-disubstituted pyridines and two pyridine-N-oxides where the pyridine rings carry a variety of alkyl, aryl, cyclohexyl, cyclohexylethyl and fluorinated-aryl substituents. The mesomorphic transition temperatures for these compounds have been measured; all the compounds show enantiotropic phases. The different substituent effects are discussed and comparisons are made with previous work on analogous systems where the hetero-function is replaced by C-F.