Siliceous materials with polymer layers formed by crosslinking of polysaccharide-polyimine mixtures have been evaluated in terms of their acid-base properties and surface charge densities. It was demonstrated that in the investigated pH region (2 < pH < 6) the materials exhibit positive surface charge and their acid-base properties depend on the crosslinking agent amount used for polymer layer formation. On the basis of the potentiometric titration data and the numerical optimisation procedure, the surface reaction equilibration constants and the share of individual reactions responsible for the surface charge creation were calculated. The investigations presented in the paper suggest that the variation of the crosslinking agent amount can modify and control transport processes of pharmaceutical substances in drug delivery not only due to crosslinking degree but also due to the charge of the polymer layer. (C) 2003 Elsevier Science B.V. All rights reserved.