As we move into a new era of lower acceptable somatic cell count levels, the prevention and control of mastitis takes on increased importance. For many years, the contagious mastitis pathogens including Staphylococcus aureus, Streptococcus agalactiae and Mycoplasma bovis were the focus of control measures primarily implemented in the milking parlor to stop the spread of these organisms from cow to cow. These contagious organisms often cause high individual somatic cell counts and ultimately high bulk tank somatic cell counts. As these high somatic cell count cows have been culled due to milk marketing regulations and more dairymen have adopted NMC recommended milking procedures, the contagious pathogens are decreasing.