This International Standard specifies a method for the enumeration of presumptive Lactobacillus acidophilus in milk products on a selective medium by using a colony-count technique at 37 °C. The method is applicable to fermented and non-fermented milks, milk powders and infant formulae where presumptive L. acidophilus is present and in combination with other lactic acid bacteria and bifidobacteria. The method is not applicable when the number of presumptive L. acidophilus is less than 104 CFU/g and the numbers of Lactobacillus rhamnosus, Lactobacillus reuteri and Lactobacillus paracasei subsp. paracasei are greater than 106 CFU/g.