The supercritical anti-solvent method was carried out in order to design sustained release systems devoted to agro-chemical compounds. This study focuses on the co-precipitation of a herbicide (diuron) and various biodegradable embedding compounds (polymers and waxes), from different organic solutions (methylene chloride and tetrahydrofuran). It is shown that, using poly(L-lactic acid) (L-PLA) as coating substance, the operating pressure has an influence on the maximum concentration of each material leading to a successful encapsulation. Besides, the particle size and morphology are modified by changing the capillary size. Other coating materials than L-PLA are tested but did not give convincing results. For instance, the best result was obtained with poly(methyl methacrylate) (PMMA) but we never succeed in obtaining non aggregated particles. The kinetics of the herbicide release in an aqueous medium shows the required effect of the coating substance, since after 20 days of immersion, only 40% of the herbicide is released. (C) 2003 Elsevier B.V. All rights reserved.