This European Standard defines general rules for the enumeration of probiotic yeasts in feed samples (additives, premixtures and feeding stuffs) that contain yeast as a single microorganism component or in a mixture with other microorganisms. The standard is not applicable to mineral feeds which are defined as complementary feedingstuffs composed mainly of minerals and containing at least 40% crude ash (Council Directive 79/373/EEC) [4]. There are different categories of feed samples: a) Additives which contain about 109 CFU/g to 1010 CFU/g (CFU = colony forming units). b) Premixtures which contain about 108 CFU/g c) Feeds, meal or pellets, which contain about 106 CFU/g and include complete feedingstuffs, and milk replacers. The detection limit is as defined in ISO 7218.