Lactoperoxidase is a milk hemoprotein that acts as a non-immunoglobulin protective protein and shows strong antimicrobial activity. Bovine milk contains about 15 and 7 times higher levels of lactoperoxidase than human colustrum and camel milk, respectively. Human, bovine, and camel lactoperoxidases (hLPO, bLPO, and cLPO, respectively) were purified as homogeneous samples with specific activities of 4.2, 61.3, and 8.7 u/mg, respectively. The optimal working pH was 7.5 (hLPO and bLPO) and 6.5 (cLPO), whereas the optimal working temperature for these proteins was 40 A degrees C. The K (m) of hLPO, cLPO, and bLPO were 17, 16, and 19 mM, and their corresponding V (max) values were 2, 1.7, and 2.7 mu mol/min ml. However, in the presence of H2O2, the K (m) values were 11 mM for hLPO and cLPO and 20 mM for bLPO, while the corresponding V (max) values were 1.17 for hLPO and 1.4 mu mol/min ml for cLPO and bLPO. All three proteins were able to inhibit the herpes simplex virus type 1 (HSV-1) in Vero cell line model. The relative antiviral activities were proportional to the protein concentrations. The highest anti-HSV-1 activity was exhibited by bLPO that inhibited the HSV particles at a concentration of 0.5 mg/ml with the relative activity of 100%.