In order to develop an implantable vehicle for enhanced control of drug release into the body, chitosan (CS) microparticles were prepared where CS was chelated by a metal ion using the emulsion coalescence technique. Aqueous solutions of CS and metal ion were separately emulsified in vegetable oil containing lecithin. After both the water-in-oil (w/o) emulsions were mixed and stirred, CS microparticles were formed as a result of gelation due to contact between the aqueous droplets of CS and metal ion. The CS microparticle formation was influenced by the stability of both the w/ o emulsions, which was dependent on the w/o ratio, the lecithin concentration in vegetable oil, and the CS types (i.e., viscosity of the CS solution prior to emulsification). These CS microparticles are expected to be useful vehicles for clinical applications, because they are prepared using only biocompatible materials and reagents. (C) 2004 Elsevier B.V. All rights reserved.