The present study has confirmed that human colostrum contains a lactoperoxidase (EC 1.11.1.7) [Langbakk & Flatmark (1984) FEBS Lett. 174, 300-303], which represents about 0.004% of the total protein in crude colostrum. An apparent 32-fold purification of the enzyme was obtained by a multistep procedure, as modified from that of the bovine enzyme, with a recovery of about 7%. By use of chromatography on an immunoaffinity column (directed against bovine lactoperoxidase B), an apparent 1450-fold purification was obtained in a single step, with a recovery of 21%. The enzyme behaved as a glycoprotein (binding to concanavalin A-Sepharose), and revealed spectral properties (Soret peak at 412 nm) and an Mr (80,000) similar to those of the bovine enzyme.