The aim of this study was to analyze changes in the expression of CD44 on bovine mammary gland lymphocytes during experimental infection caused by peptidoglycan of Staphylococcus aureus. Lymphocytes were obtained by lavage of the mammary glands at four intervals (24, 48, 72 and 168 hours) following experimental intramammary injection of peptidoglycan. The percentage of CD44 positive lymphocytes peaked at 24 and 48 hours following infection with peptidoglycan of Staphylococcus aureus. The results show that during the experimental infection the expression of CD44 on lymphocytes is induced in early stage of mastitis (till 48 hours from the stimulation of inflammation). In the resolution of mastitis, CD44 expression is dramatically decreased.