Анотация: Somatic cell count, viability of cells and percentages of the cell subsets (CD45, granulocytes, monocytes/ macrophages, CD4, CD8 and B lymphocytes) were determined in milk from uninfected cow udder quarters (n = 7) and from quarters infected with S. aureus (n = 18). Cell subpopulations were double labelled with monoclonal antibodies and determined by flfl ow cytometry. Percentages of epithelial cells, polymorphonuclear granulocytes, monocytes and lymphocytes were determined by light microscopy in stained smears. The SCC, percentages of cells labelled with antibodies specififi c to CD45, granulocytes, CD4 and CD8 epitope were statistically different between infected and uninfected quarters. The percentages of cells obtained by light microscopy were statistically different between the infected and uninfected groups. The percentages of granulocytes in infected animals were associated with the age and gravidity of the animals. Within the infected group, the percentage of CD8 varied statistically between imported replacement cows and animals raised on the farm. Values of epithelial cells and CD45- were moderately correlated (Pearson`s r = 0.47). The percentages of granulocytes obtained by the two methods were also moderately correlated (Pearson`s r = 0.52