The catalytic effect of enzymes in different environments has been compared. Biodegradable polyesters and corresponding nanoparticles have been synthesized by an "eco-friendly" technique; enzyme-catalyzed ring-opening polymerization of lactones in bulk and in an aqueous mini-emulsion. Lipases from Burkholderia cepacia (lipase PS), B. cepacia immobilized on ceramic, Pseudomonas fluorescens and Candida Antarctica have been used as catalysts in the polymerization of L-Lactide (LLA), pentadecanolide (PDL) and hexadecanolide (HDL). The reaction conditions during the bulk polymerization of LLA were varied by adding different amounts of ethylene glycol at 100 degrees C or 125 degrees C. A number average molecular weight (M-n) of 78,100 was obtained when lipase PS was used at 125 degrees C. Lipase PS had a high catalytic activity in an aqueous environment with 100% conversion in 4 h, and the nanoparticles obtained from mini-emulsion polymerization were between 113 and 534 nm in size. The amount of hydrophobe affected the size of the PDL nanoparticles produced, less than the amount of surfactant in both systems. (C) 2010 Elsevier Ltd. All rights reserved.