Novel drug delivery technologies have now evolved to allow the clinical production of new dosage forms. One new form, biodegradable microspheres, may have utility as a second-generation formulation for parenterally administered proteins and peptides br may be required for the success of some new chemical entities. Here, we have focused on the use of poly(lactic-co-glycolic acid) (PLGA) microspheres to provide a continuous delivery of therapeutic proteins or a pulsatile delivery of protein-based vaccines. To date, our success with solvent evaporation processes has been primarily in the production of microspheres with a triphasic protein release pattern instead of a continuous release. However, with continued development efforts, this method may be used to produce continuous release protein formulations. While this review draws from our own work, there is a great deal of excellent research in this area at both universities and industrial laboratories. This work combined with our studies indicates that this technology holds much promise for new protein formulations that will provide improvements in patient care and, perhaps, increased efficacy.