The extensive use of pasteurization with various dairy products, for the destruction of disease-producing organisms that may be present and for the improvement of the keeping qualities, suggests that the process may have important advantages in the cheese industry. Cheddar cheese made from pasteurized m.ilk with the usual cheese cultures tends to ripen slowly and lack flavor and aroma so that, if a desirable product is to be obtained, the use of additional cultures in the milk seems necessary. Bacteriological studies on cheddar cheese made from raw milk have shown that Lactobacillus casei commonly grows extensively in the product and that often enormous numbers are present after some weeks of ripening. These results suggest that there may be an advantage in adding L. casei to pasteurized milk to be made into cheddar cheese. This is especially true when the pasteurization exposures are high enough to insure the destruction of any disease-producing organisms present. Such exposures would be expected to destroy a large percentage of the total organisms in the raw milk. In the past much of the pasteurized milk made into cheddar cheese in certain areas has been flash pasteurized at relatively low temperatures, the primary purpose being to control objectionable fermentations in the cheese.