A definition is proposed for the interquarter ratio of markers of inflammation in the bovine mammary gland which in contrast to present measurement procedures has well-defined distributional properties and thus facilitates statistical analysis. Our proposal of an interquarter ratio is equally applicable to evaluation of both single and multi-sample experiments. Finally, we define a new index for diagnosis of subclinical mastitis at the cow level, the interquarter variation, which assesses the degree of dispersion of the four quarter levels for values of any continuous inflammatory marker.