Numerous attempts to develop in-line Systems for the measurement of the electrical conductivity of milk as an aid to the detection of mastitis have been described. The major technical problem of fouling of electrodes exposed to milk has been overcome in the sensor tested here by use of an inductive System of measurement. The practical application of this System in the milking parlour is reported. The novel mastitis sensor has been shown to detect incipient mastitis before there are visible signs of abnormal milk. Conductivity measurements have the advantage over other diagnostic procedures in that the information is available immediately without additional effort. Normalized conductivity and milk yield variation results indicate the potential for developing a practical, automatic System for mastitis detection.