a novel hydrophobic polymeric matrix is provided which is suitable for use after implantation in vivo in a subject for the controlled release and delivery of biologically active substances such as drugs , antibiotics , steroids and the like . alternatively , the matrix can be used outside the body for release of fragrances , pesticides and the like . the implantable matrix comprises a polymeric polyanhydride formulation whose internal anhydride linkages are hydrolytic in nature in varying degrees in accordance with the chemical composition of the backbone , ph and temperature of the environment . as the individual anhydride linkages become hydrolyzed , the matrix erodes predominantly by surface erosion into non - toxic biocompatible degradation products with concomitant release of the biologically active substance .