Macromolecular interpolymer complexes were prepared by blending concentrated equimolar solutions of chitosan and poly(4-N-methacrylamidobenzoic acid) and evaporation of the solvents. The products obtained presented the structure of interpolymer complexes as indicated by FTIR spectroscopy. The thermal treatment of the solid products at 120 degrees C gives rise to a partial dehydration together with the formation of covalent amide bonds between both polymeric components. The sorption behaviour of the systems is analysed on the basis of the structure of the macromolecular systems and a consideration of Fickian behaviour for highly hydrophilic materials. The diffusion coefficients determined are dependent on the thermal treatment applied to the interpolymer complexes.