This part of ISO 13366|IDF 148 specifies a microscopic method (reference method) for the counting of somatic cells in both raw and chemically preserved milk. This part of ISO 13366|IDF 148 is applicable for the counting of somatic cells in cows' milk, provided that the eventually mentioned prerequisites are met. This method is suitable for preparing standard test samples and determining reference method values that are required for calibrating mechanized and automated cell-counting methods. WARNING - The use of this standard may involve hazardous materials, operations and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.