Summary The microbiological changes on the surface of ripening New York State limburger cheese as found by microscopic examinations show a very definite sequence. Budding yeasts appear in from two to three days and are found in large masses in four to five days. At this stage the surface of the cheese becomes slimy and the organisms in this slime are distributed evenly over the surface by rubbing the cheeses with the hands. About the sixth or seventh day short slender rods ( Bacterium linens Weigmann) appear and increase to large numbers about the eighth day when they are evenly distributed over the whole surface. There is little doubt but that these organisms are responsible for the reddish color which appears on the cheese at this time. The slime on the surface then becomes heavier and is about the consistency of soft butter. From ten to eighteen days the yeast cells tend to decrease in size, become distorted and disappear entirely. Very few yeast cells were to be found on the older cheeses. Other types of microorganisms, though present from time to time, do not appear to have any important part in the ripening of the limburger cheeses.