WE HAVE PREVIOUSLY reported general methods for the extraction of the gonadotropic hormones from acetone desiccated pituitary tissue and the fractionation of the extract into two gonadotropic fractions (1, 2, 3, 4). One of these preparations (FSH) produces follicular growth in the ovaries and tubular development in the testes while the second (LH) produces cor′ pora lutea if injected with the FSH or if given to animals whose ovaries have undergone considerable follicular development. This preparation does not produce follicles or corpora lutea when injected alone into sexually immature, 2i′dayold, or hypophysectomised rats. In the male, this preparation acts on the interstitial elements of the testes causing secretion of male hormone, resulting in hypertrophy of the secondary sex glands. Because of the selec tive action of these two preparations on the male and female gonads, we con′ eluded that each preparation contained a separate gonadotropic hormone and that the gonadotropic activity of the pituitary ...