As a result of experimental research conducted in these laboratories and data obtained in factories in the Swiss cheese-producing areas in Wisconsin, Ohio, Idaho, and Pennsylvania, much information has been collected with respect to causes of variations in quality of Swiss cheese. I t was shown, in results published previously (3), that the use of milk of poor bacteriological quality (methylene blue reduction time less than 3 hours) resulted in a decrease in the average grade of the cheese, and also that a complete lack of ripeness in the milk was apparently detrimental. In a recent report (4), methods were described which can be used to control the amount of moisture in the green cheese, and it was demonstrated that methods used to reduce the percentage of moisture resulted in a general improvement in quality of cheese. This paper deals with the relationship between the percentage of fat in dry matter in the cheese and its quality, and with procedures used in predicting the percentage of fat in dry matter in the cured cheese.