Studied was the extent to which lipolytic changes took place in milk in dependence on the subclinical diseases and the secretory alterations of the mammary gland in cows. A copper saponifying method was employed to determine the amount of the free fatty acids in the milk from the affected and normal quarters of a total of 60 cows. It was found that there was a definite correlation between subclinical mastitis and the extent up to which lipolytic changes took place in milk fats. The average content of the free fatty acids in the milk obtained from the diseased quarters of the under was 7.28 mg%, while the milk from the normal quarters contained them in an average amount of 3.96 mg%. In cows having secretory disturbances of the mammary gland there was certain rise of the free fatty acids as against the cows with normal quarters, however, the higher values were mathematically insignificant (P=0.1). It is believed that the lipolysis of milk fats is effected within the mammary gland as the result of the action of serum factors, and not of the effect of cellular lipase.