Abstract IT has been established that there is an interaction between the secretions of the gonad and the anterior pituitary. The gonadotropic content of the anterior pituitary of pullets at various levels of egg production has been studied in several laboratories (Phillips, 1942; Nakajo and Imai, 1957). Genetic differences in the concentration of gonadotropins in the anterior pituitary have been shown by Van Krey and Siegel (1968) whereas Nalbandov and Card (1942) and Munro et al. (1947) demonstrated genetic differences in response to secretions of the anterior pituitary. Further, a genetic difference in weight responses of the testes of chicks to purified FSH but not to LH was found by Siegel and Siegel (1961). Age at sexual maturity is influenced by the secretion of gonadotropins. Stocks which differ in age at sexual maturity might be expected to differ in gonadotropin secretion, target organ response or both. Siegel (1962) has developed lines . . .