Supercritical processes for drug delivery system design have attracted considerable attention recently. This present work investigates the application of a supercritical antisolvent coating process for controlled drug release design. Hydrocortisone as the host drug particles and poly (lactide-co-glycolide) (PLGA) as the polymer carrier were selected as the model system for this purpose. In this research the drug particles were suspended in a polymer solution of dichloromethane. The suspension was then sprayed into supercritical CO2 as an antisolvent. A parallel study of co-precipitation of the drug and polymer using the same supercritical antisolvent process at the same operating conditions was performed for comparison with the coating process. SEM images were used to characterize the drug particles before and after and the assay analysis was carried out using HPLC. The coated particles and co-precipitated particles were evaluated in terms of encapsulation efficiency and drug release profiles. The major advantage of this new approach is the ability to physically coat very fine (<30 mu m) particles without having to dissolve them in an organic solvent. It was found that higher polymer to drug ratios produced higher encapsulation efficiencies and the coated drug particles did show sustained release behavior. The co-precipitation of the drug and polymer (at the same operating conditions), however, did not exhibit any sustained release. (C) 2006 Elsevier B.V. All rights reserved.