This cytochemical investigation is proposed to provide basic information about location of sites of synthesis and storage of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in the pituitary gonadotropin cells. We will determine if such sites differ with respect to sex of the animal and if they are distributed similarly throughout the gland. This information will be obtained via a quantitative immunocytochemical technique (the unlabeled antibody peroxidase-antiperoxidase technique) at the electron microscopic level in which specific LH and FSH antisera purified by affinity chromatography are used. We will also obtain cytochemical information about the interaction of the gonadotropin cells with LH-releasing hormone (LH-RH). Target organ immunocytochemical localization of LH-RH at the electron microscopic level will define which gonadotropin cells bind with the releasing hormone and if such reactions vary with respect to sex, and during different stages of the oestrous cycle. Thus, we will both cytochemically identify the cells which interact with LH-RH and also their hormone content. This information must be obtained before cytophysiologists can adequately design experiments to test physiologic or pharmacologic agents affecting release of gonadotropins. The information is also basic to an understanding of the mechanisms of storage and secretion of LH and FSH and their alpha and beta chains. Bibliographic references: Moriarty, Gwen C. Electron Microscopic- immunocytochemical studies of rat pituitary gonadotrophs: a sex difference in morphology and cytochemistry of LH cells. Endocrinology, In Press, June, 1975; Moriarty, Gwen C. Subcellular localization of luteinizing hormone in the rat anterior pituitary: a sex difference in the morphology and cytochemistry of LH gonadotrophs. Anat. Rec. 181: 430, 1975.