Proteins are an integral part of the body as they perform important physiological and biological processes such as signaling, biotransformations, transcription, translation, receptors for pharmacological response elucidation to name a few . Several disorders are associated with a complete absence of specific proteins within the body or their occurrence at sub-optimal levels. Under such circumstances the delivery of the associated protein as a therapeutic agent via an external means may help alleviate the disease. Some of the disorders that may be treated by employing this class of agents include cancers, autoimmune diseases, cardiovascular and metabolic diseases, mental disorders and hypertension. Unfortunately, the use of proteins as therapeutic agents is severely restricted by problems associated with their delivery and retention of activity upon delivery. This necessitates the development of a specialized controlled delivery system capable of overcoming these drawbacks. Biodegradable polymeric microparticles have been investigated successfully for such sustained delivery applications. The goal of our research was to develop such a microparticle type controlled release system for the delivery of vasoactive intestinal peptide (VIP) and aprotinin using a novel L-tyrosine based polyphosphate polymer designated as poly (DTH-EP). Blank microparticles or microparticles loaded with either protein were fabricated using a conventional water-in-oil-in-water emulsion technique. Microparticles loaded with a model protein, FITC-bovine serum albumin were also prepared using a similar method. These particles were characterized for surface morphology, size distribution, protein distribution within the particle core and in vitro hydrolytic degradation. Loading studies and in vitro release studies of the encapsulated proteins were also performed. Scanning electron microscopy (SEM) results showed that the microparticles had a slightly rough surface morphology but were free of any gross surface defects such as pores. Light scattering results corroborated results obtained from preliminary size distribution analysis performed using SEM and the particles were found to show a relatively narrow distribution between 2-10µm. In Vitro hydrolytic degradation studies performed using blank microparticles showed that the particles degraded completely over a period of 8 days, possibly via a bulk-hydrolytic degradation mechanism. These results match very well with in vitro degradation studies performed using poly (DTH-EP) films where approximately 80% mass loss was found to occur over a period of 7 days . Preliminary protein distribution studies performed using fluorescence optical microscopy of particles loaded with a model FITC-BSA protein showed that the protein distributed uniformly within the core of the particles formed via a w/o/w emulsion technique. Confocal laser scanning will also be used to validate these results. Finally, in vitro release studies of FITC-BSA were performed and the release samples were analyzed spectrofluorometrically. A complete release of FITC-BSA was observed to occur over a period of 7 days from within the poly (DTH-EP) microparticles. The release studies with bovine VIP and bovine aprotinin have also been performed and the results will be analyzed using HPLC or an ELISA based assay. Thus, a microparticle type controlled delivery system for the short term delivery of therapeutic agents such as proteins has been successfully synthesized using a novel L-tyrosine based polyphosphate.