Prochiral dimethyl or diethyl phenylmalonate were partially hydrolysed to the corresponding chiral monoesters by different immobilized preparations of lipase from Thermomyces lanuginosa. This enzyme does not hydrolyse the monoesters and hence its hydrolysis was carried out without production of the final achiral di-carboxylic acid, quantitatively yielding the chiral monoester. Asymmetry factor with preference towards to production of the (+)-isomer could be increased from 1.5 up to 10 depending on the immobilized preparation, the type of acyl donor and the presence of co-solvents. Thus, different immobilized preparations of the same lipase, when acting at different experiment conditions, may exhibit a very different activity and enantioselectivity. Furthermore the presence of small concentrations of detergents (from 0.01 to 1%) in the reaction media exerts dramatic effects on the activity and enantioselectivity of TLL immobilized on conventional supports (e.g., covalently immobilized on CNBr-activated agarose). The presence of Triton X-100 has strong inhibitory effects and hardly modifies the enantioselectivity of the derivatives. However, a cationic detergent (CTAB), promotes very significant improvements of activity (by a 40-fold factor) and enantioselectivity (from 3.5 to 20). Under these conditions a highly enantioselective asymmetric hydrolysis, obtaining the (+)-1-(ethoxy-carbonyl)-phenylmalonic acid with an e.e. over 90% can be obtained. (c) 2006 Elsevier Inc. All fights reserved.