A biocompatible system was developed that permits continuous release of biologicallyactive insulin from small polymer matrices. Powdered insulin particles were incorporated into an ethylene-vinyl acetate copolymer matrix. The presence of particulate insulin resulted in a matrixcomposed of tortuous channels and constricted pores through which release occurred. When aqueous release media permeated the matrix, the insulin dissolved and diffused slowly through this tortuous network. The large concentration of insulin within the matrix provided the driving force for release. Release kinetics from these insulin polymer matrices were enhanced by increasing the insulin solubility, the insulin powder particle size, the loading of insulin within the matrix, and the porosity of the matrix. Appropriate geometric design of the polymer matrix resulted in near-constant insulin release rates.