The aim of this investigation was to study and estimate the dimensional changes, gel evolution, swelling, and erosion of chitosan lactate mixture tablets with Polyox or Ethocel, in distilled water and 0.1 N hydrochloric acid (HCl) solution, using an image analysis method. This method permits the accurate measurement and evaluation of dimensional changes, core changes, and gel growth. All tablets displayed greater dimensional expansion in water than in HCl. The fastest and greatest swelling was exhibited in water, whereas, in contrast, the greatest erosion was observed in HCl. Chitosan/Polyox tablets exhibited greater expansion, swelling, and gel growth than the equivalent chitosan/Ethocel tablets. The thickness of the gel layer in chitosan/ Polyox tablets, particularly, increased considerably with time up to 8 h, indicating that the development of a thick and durable gel barrier is a characteristic necessity for the preparation of sustained drug release delivery systems. In addition, the differentiation of the above-mentioned characteristics in relation to changes in pH values also gives useful information about sustained release preparations made from these polymers, since it is well known that the gastrointestinal tract is characterized by a range of pH values. In general, the polymer mixtures studied comprise a useful and promising combination of materials for the development and manufacturing of sustained release devices based on these polymers. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 110-121, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20208