In order to develop glucose sensitive insulin delivery systems, several researchers proposed reservoir systems consist of immobilized glucose oxidase in a pH responsive polymeric hydrogel, enclosing a saturated insulin solution. The objective of this study was to evaluate a matrix system in which the drug and the enzyme are uniformly distributed, throughout a solid polymer. Hydrogels with immobilized glucose oxidase display faster and higher swelling and release rates at higher glucose concentrations. Similar results were obtained for bacitracin release. The release rates increase when the pH step is from the higher value to the lower and decrease when the change is in the opposite direction.