The effect of basal hypothalamic electrolytic lesions in various regions on the pituitary cytological organization and staining characteristics was studied in White Leghorn cocks. The pituitaries were stained with PAS, Masson trichrome, Azan and Alcian Blue, PAS, Orange G. The pituitaries of all hypothalamic lesioned birds were significantly smaller than those of the controls. Cocks, with lesions located in the mammillary nuclei and posterior part of the ventromedial nuclei, with complete atrophy of testes and combs (FC), demonstrated total chromophobic appearance in all staining procedures used. Cocks bearing lesions in the posterior part of the mammillary nuclei, covering sometimes a part of the arcuate nuclei, with atrophied testes but carrying large combs (FCLC), showed a considerable decrease in all typical stainable cells in the pituitary as compared to the controls. Lesions located mainly in the ventromedial nuclei, causing a slight decrease only in the gonadal weight (OGD), did not affect the cytological organization and staining characteristics of the pituitary. Based on the existence of immunological reaction between chicken LH and anti HCG, Pregnosticon (commercial anti-HCG, Organon) was used as antibodies in a direct immunofluorescent method for the possible demonstration of LH producing cells in the cocks' pituitary. No immunofluorescent reaction was found in the pituitaries of the FC cocks. On the other hand, in the pituitaries of the control and FCLC cocks, the number of cells which reacted with the immunological conjugate were in accordance with the cocks' androgen activity, which might imply on the LH secretion rate.