Novozym 435 is a widely used immobilized preparation of lipase B from Candida antarctica (CALB). This preparation is quite stable in the presence of hydrogen peroxide compared to other proteins and has been used for the preparation of peracids. However, its stability is still a limitation in the design of reactions under these harsh conditions. In this paper, we show an alternative CALB preparation that is far more adequate for this medium by immobilizing the enzyme on hydrophobic octadecyl Sepabeads. This preparation retained 55% of the initial activity after 4 days of incubation in 10 M hydrogen peroxide at 22 degrees C, while Novozym 435 maintained only around 15% after only 24 h. All assayed preparations of the lipase from Rhizomucor miehei were fully inactivated after 4 h in 5 M hydrogen peroxide, suggesting that this enzyme was by far less stable than CALB. Moreover, the lost CALB activity may be partially recovered by incubation of the oxidized CALB sample with sodium borohydride. Also, it has been shown that native electrophoresis may be a simple tool that can be used to study the intensity of the modification caused by hydrogen peroxide. CALB from Novozym 435 increased its electrophoretic mobility in this experiment, while the mobility of the enzyme immobilized on octadecyl Sepabeads remained almost unaltered; this confirmed that the enzyme immobilized on this support was not as extensively modified by hydrogen peroxide. (c) 2010 Elsevier Ltd. All rights reserved.