Polymers containing amidine groups -NH-CR=N- (R: -H, -CH3, -C6H5) in the main chain were characterised by inverse gas chromatography. In dependence on the residue R the dispersive contributions of the surface free energy were determined. From interactions with polar probe molecules the Lewis acid-base properties of the polymer surfaces were concluded. Semiquantitative K-A- and K-B-parameters describing the possibility of the stationary phase to act as electron donor or acceptor showed that polyamidines are Lewis bases. The results were discussed with respect to the conformation of the amidine group and interactions between the polymer chains. (C) 2001 Elsevier Science Ltd. All rights reserved.