The distribution and development of bacteria during the maturing of New Zealand Cheddar cheese have been studied using stained sections of cheese. The starter streptococci usually occur singly and in small groups throughout the mass of the cheese, their distribution on a microscopic scale being very irregular. In contrast, the bacteria developing later form discrete microcolonies, most of which are associated with the curd junctions. Instead of adding lactobacilli to milk, smaller numbers may be added to the dry curd before cheddaring or after milling. Some observations on the physical structure of cheese are made.