Propofol (2,6-diisopropylphenol) is a hypnotic intravenous agent with in vivo antioxidant properties. This study was undertaken to examine the in vitro effect of propofol on lactoperoxidase (LPO; E.C. 22.214.171.124) obtained from bovine milk. Lactoperoxidase was purified with three purification steps: Amberlite CG-50 resin, CM-Sephadex C-50 ion-exchange chromatography and Sephadex G-100 gel filtration chromatography, respectively. Lactoperoxidase was purified with a yield of 21.6%, a specific activity of 34 EU/mg proteins and 14.7-fold purification. One enzyme unit is defined as the oxidation of 1 mol ABTS per min under the assay condition (25 degrees C, pH: 6.0). To determine enzyme purity, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed and single band was observed. The effect of propofol on lactoperoxidase were determined using 2,2'-azino-bis (3-ethylbenzthiazoline-6 sulfonic acid) diammonium salt (ABTS) as a chromogenic substrate. The IC50 value of propofol was found as 15.97 M. Also, K-i constant for propofol was 3.72 M and propofol was found as competitive inhibitor.