The swelling behaviour of poly(acrylic acid) microspheres, produced from poly(acrylic acid) crosslinked with maltose, was investigated as a function of time by using a laser diffraction spectrometer. Swelling was also studied in various pH glycoprotein solutions. Microscopy revealed cofirmatory evidence of interfacial film formation when microsphere hydration occurred in a pH 5 glycoprotein solution. ATR-FTIR spectroscopy was used to determine the diffusion coefficient of water through the interfacial film existing at the poly(acrylic acid) glycoprotein solution interface. Both processes exhibited a pH dependency with rates decreasing in the sequence pH 7 > 6 > 5 = 4. (C) 1998 Elsevier Science B.V. All rights reserved.