The objective of this thesis was to evaluate the blood and milk concentrations of lipopolysaccharide-binding protein (LBP) from cows with naturally-occurring mastitis as biomarkers of this disease. Milk and blood samples were collected from 101 clinically healthy dairy cows and 17 dairy cows with clinical mastitis. The concentrations of LBP, haptoglobin and serum amyloid A (SAA) were determined in these samples by enzyme-linked immunosorbent assay. Both LBP and haptoglobin concentrations were higher in the milk and blood of quarters and cows with clinical mastitis respectively than in those that were healthy. Whereas haptoglobin concentrations differed between uninfected and subclinically-infected quarters, LBP concentrations only differed between them when milk somatic cell counts were low. Unlike haptoglobin and SAA, blood concentrations of LBP in cows with a subclinical intramammary infection were not significant from those of cows with all healthy quarters. Thus, haptoglobin may be a preferred biomarker of subclinical intramammary infection.