The original experiments, done by Witschi and his associates, on sexual differentiation of pituitary gonadotropins weie interpieted as demonstrating the contrasting effects of testes on the subsequent output of luteimzing hormone (LH) and interstitial cell stimulating hormone (ICSH). The subsequent demonstration that these two hormones were identical has led to a theory that testes alter the hypothala mic centeis which control the cyclic release of LH “Masculinization of the female hypothalamic pituitary axis has been claimed following neonatal treatment with steroids”. However, true sex reversal of gonadotiopin patterns has neither been demon stiated, the male pattern has not yet been clearly denned Consistent high levels of blood and pituitary follicle stimulating hormone (FSH) appear to be at least two characteristics of the male pattern, and neither can be induced in lemales by neonatal treatment with testosterone propionate. Furthermore, castration of males at bnth with concomitant ovanan implinldtion, does not appear to remove the male pattern of high FSH. Considering that we understand so little regarding gonadotropin patterns in males, we cannot assume that this pattern can be induced simply by pie or postnatal steroid trealment. Considerably more data on the positive and negative feedback effects of steroids, and steroid combinations, on TSH, LH, and piolictin in both males and females, will be requned before a meaningful concept of sexual differentiation cin be formulated