For a survey of the numbers of lactobacilli present in milk used for cheese-making in creameries, counts were made on an acetate-agar medium (1) selective for lactobacilli. It was observed that the numbers of lactobacilli in the milk in the cheese vat sometimes greatly increased after the addition of the starter to the milk. When these starters were plated on acetate agar growth of lactobacilli, sometimes in large numbers, suggested contamination of the starters with these organisms. The starters in use at sixteen different creameries were then examined on acetate agar, and seven were found to contain lactobacilli. Representative colonies of these organisms were picked from each starter and these strains identified physiologically using the methods of Briggs(2) and Wheater(3,4), and serologically using the group sera of Sharpe(5) and Sharpe & Wheater(6). Table 1 shows the numbers and species of lactobacilli present in the starters. Each starter was sampled several times, usually at monthly intervals.