This part of ISO 13366 / IDF 148 gives guidance on the operating conditions for counting somatic cells in both raw and chemically preserved milk, using fluoro-opto-electronic somatic cell counters in which either a rotating disk technique or flow cytometry is applied in the counting section.The guidance is applicable for the counting of somatic cells in raw cow milk. The guidance is also applicable for the counting in raw milk of other species such as goat, sheep and buffalo, if the mentioned prerequisites are met.