The lipolytic bacteria in milk, cream and butter are of interest from the standpoint of the development of defects in these products. Presumably, rancidity is the most important of such defects, although since many of the lipolytic bacteria also attack constituents of milk other than fat, additional defects may be involved. Comparatively little attention has been given to the numbers of lipolytic organisms in various dairy products, because methods of determining these organisms have not come into such common use as have the methods of determining proteolytic and acid-forming organisms.