In connection with aim of maximizing the bio-availability of conventional drugs with minimum side-effects, new drug delivery systems (DDS) continue to attracted much attention. The controlled or sustained release of drugs represents one such approach, and in this regard report upon a study of DDS using biodegradable polymers which include poly (lactic acid) (PLA), poly (glycolic acid), and their copolymers (PLGA). Much attention is being paid to the controlled release of bio-active agents from microcapsules and microspheres made of biodegradable polymers, such as lactic acid homopolymers, as well as copolymers of glycolic acid. (11-21) Microcapsules or microspheres are injectable and able to provide pre-programmed durations of action, offering several advantages over the conventional dosage forms. This article reviews the results of a work program conducted in collaboration with a medical doctor upon DDS using biodegradable microspheres, such as PLA and PLGA.