A key issue in drug delivery is the design of suitable platforms for controlled release that avoid bursting effects and attain controlled release profiles throughout the lifetime of the device. The delivery characterisitics of injectable polymer solution and microparticle systems, as well as film coated systems are strongly dependent on the membrane structure of the polymer carrier phase. The latter is in turn largely determined through the interplay among drug, polymer, and solvent properties during and after fabrication of the device. In all these cases the membrane structure forms by the process of phase inversion. Our studies are exploring systems that include biostable and biodegradable polymers, volatile and non-volatile solvents, and hydrophobic and hydrophilic drugs. Electron microscopy, x-ray diffraction, scanning calorimtery, and chromatography are used to characterize the membrane-drug interactions and strucutre. These data are combined with release rate experiments using standard dissolution devices to correlate release kinetics with the above mentioned variables. Modeling of the release kinetics is also being carried out.