Mastitic milk was detected by obtaining conductance measurements using an impedance microbiology Bactometer® 120 SC instruments. Conductance readings taken after 30 min at 25'C separated normal and abnormal milks when readings differed by more than 3% from the variance among instrument module wells. Samples blended from four quarters of a cow indicated milk from one quarter was abnormal if the salt level in the abnormal quarter raised the blend conductivity above that of normal samples and variance among the wells. Either solid or liquid substrates that contained bacterial stimulants could be used to accelerate bacterial acid production or to reduce impedance detection times, each without adversely affecting the ability to detect abnormal milk. However, measurements with liquid substrates varied with the volume of sample in the well. Results suggested that a fixed volume of one ml be used. Such a volume would allow simultaneous detection of abnormal milk and bacterial load on the same sample.