The use of polymeric particles as devices for the controlled release of active agents is attractive not only for application in humans, but also in the veterinary field. Studies on the production and characterization of poly(lactic acid) (PLA) particles incorporating or not 17 alpha-methyltestosterone (MT), a hormone frequently use for the sexual reversion of Nile tilapia raised in large scale in tanks are herein reported. The particles were obtained employing a supercritical anti-solvent (SAS) method, using dichloromethane (DCM) as solvent for the polymer and the hormone and CO2 as the supercritical fluid. The influence of the operating pressure, polymer solution concentration and flow rate on the size and morphology of particles was evaluated, as well as the effects of the incorporation of the hormone at different MT/PLA mass ratios. The results attained showed that the PLA particles presented appropriate DCM concentrations levels (below 600 ppm) and average diameters between 5.4 and 20.5 mu m when free of the hormone. The average diameters of the particles containing 17 alpha-methyltestosterone increased up to 4 times, and MT incorporation efficiencies up to 53% were achieved. A significant decrease was noticed in particle crystallinity (from 26.52 to 1.72%) due to the addition of the hormone to the formulation. X-ray diffraction analysis showed no separate diagrams of each substance as a result from the physical mixture of the polymer with the hormone. The particles obtained had low zeta potential values, what indicates reasonable tendency to agglomerate. MT release studies performed at different pH conditions (2.2, 5.0, 7.4 and 8.8) showed that the particles presented appropriate stability for the intended use. (C) 2013 Elsevier B.V. All rights reserved.