Aqueous suspensions of modified cinchonidine platinum nanoparticles produced from H2PtCl6 reduction in the presence of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride salt have shown efficient activity for the asymmetric hydrogenation of ethyl pyruvate in biphasic media under hydrogen pressure. The aqueous phase containing the Pt(0) nanocatalysts can be used for further runs with a total conservation of activity and enantioselectivity for (R)-(+)-ethyl lactate up to 55%. Characterization of the reusable catalytic system by transmission electron microscopy revealed the formation of a "colloidal superstructure." (C) 2004 Elsevier Inc. All rights reserved.