Microparticles containing 5-fluorouracil (5-FU) were prepared using poly(DL-lactide-co-glycolide) with an oil-in-oil emulsion/solvent extraction technique. Particle characteristics including size distribution, 5-FU loading efficiencies, in vitro release and degradation were investigated. The dispersed phase was composed of PLG dissolved in dichloromethane, and the continuous phase was paraffin oil containing lecithin. 5-FU was successfully entrapped in the microparticles with trapping efficiencies up to 76%, loading level 10% w/v, and particle size 3 mum. Release profiles of 5-FU loaded microparticles were determined to follow a first-order-time relationship. An optimized preparation of 5-FU microparticles was achieved and was capable of controlling the release of 5-FU over 21 days with an in vitro delivery rate of 0.4 mug 5-FU/mg particles/day in the study. Preliminary animal studies indicated that the 5-FU loaded microparticles as an ocular delivery system showed no ocular toxicity and no significant inflammatory response in rabbits for 2 months. The 5-FU loaded microparticles approach, with PLG, might be a potential for the application of long-term delivery of hydrophilic drugs in the eye.