The milk regulations in most progressive areas require that milk shall be from one or more healthy cows; that it shall be practically free of colostrum; and that milk otherwise abnormal should not be offered for sale. The screening tests described in this booklet are all based on the number of leucocytes in the milk. They are four which are currently in common use, as well as a recent modification of the CMT test. The Milk Quality Test (MQT)has not been included in this publication because of the scarcity of well-documented, scientific reports concerning the significance of positive results in terms of leucocyte counts.