lndivrdual normal and mastitic milk samples were collected from healthy and udder infected cows Milk samples were subjected to polyacrylamide gel electrophoretic analysis in order to monitor any conSiderable changes in milk proteins At the same time, samples were analysed for the concentration of immune system factors which increase in milk after infection of the udder These factors include immunoglobulinG (lgG). lysozyme (L2) and iactoferrin (LF) The obtained results revealed that ccncentrations of IgG. L2 and LF were markedly increased with mastitis incidence and increase in concentrations was mastitis-degree dependent Since in first degree mastitic milk the concentrations of L2. LF and IgG were increased by 1 2. 1 5 and 1 3 times, respectively. than in normal milk. Eut in second and third degrees their concentrations increased by i 3 7 6 71 t4], 13 3) and ( 1 5. 1 8) times for L2. LF. and lgG respectively This result revealed that among the immune proteins, LF and L2 not lgG were highly affected by inflammation of the udder The electrophoretic patterns of normal and mastitic milk were completely distrngurshable, Since the intensities of B- and ds—casein bands were markedly decreased in mastitic milk and the decrease was mastitis degree dependent. On the contrary the intensities of Bovrne Serum Albumin (BSA), IgG ard LF band were obviously increased in mastitic milk and were positive correlated to degree of mastitis. Meanwhile, some unique peptides were revealed in patterns of second and third degrees of mastitic milk. not present in both normal and first degree mastitic milk They have molecular weights of 21 2 49.8. 54 2 7'8 4 and 82 2 kDa This means that they are related to the intenSity of udder inflammation, therefore these peptides can be used as biomarkers for detection of mastitic milk. From these findings it can be concluded that the differentiation not only between normal and mastitic milk but also for detecting the degree of mastitis. can be ea5ily achieved,