The local motions of aryl-aliphatic polyesters based on ethylene glycol and hydroxybenzoic acid or isophthalic acid were investigated in chloroform and trifluoroacetic acid/dichloromethane solutions using C-13 n.m.r. Measurements of the C-13 spin-lattice relaxation times have indicated the existence of hydrogen-bonding interactions between the carboxyl groups of the polymers and the solvent in the trifluoroacetic acid/dichloromethane mixture. Interpretation of the C-13 spin-lattice relaxation times in terms of segmental main-chain motions was carried out using the Dejean-Laupretre-Monnerie orientation autocorrelation function. The internal motions of the aromatic rings have been described in terms of jumps between two equilibrium positions for the hydroxybenzoic rings and by stochastic jump processes for the isophthalic rings. The energy barriers determined for these motions have been compared with those measured in related systems or estimated from conformational energy calculations.