Summary.Investigations on the relation between morphological factors and the presence of hyaluronidase in bull testes are described. A very close correlation has been found to exist between the activity of the spermiogenesis and the hyaluronidase content. It would seem, however, that complete spermiogenesis is not required for the production of hyaluronidase. Thus the presence of hyaluronidase probably is a condition for fertility, but its occurrence is notper sean indication of the capacity to fertilize.The size and the dry substance content of the testis possess a certain correlation with the hyaluronidase content.The formation of hyaluronidase in cells in general is discussed.