The results of this experiment provide some support for Broverman's (1968), activation/inhibition theory and the theoretical position of I3awson (1972), as the normal sex based cognitive abilities of the white rat have been reversed by neonatal sex hormones and gonadectomy. Thus while the normally higher level of activation in the female rat was depressed by masculinization, p<.001, the lower level of male activity was increased, p<.05. Furthermore, the normal male higher spatial Symmetrical Maze Learning was depressed by oestrogen injection, p<.005, while the lower female spatial learning has also been stimulated by neonatal masculinization, p<.005. These findings thus have considerable significance for the psychology of individual differences, as they confirm the effects of sex hormones at critical periods of development on subsequent sex-based cognitive abilities. However the effect was not as great for spatial learning while the nature of the design did not permit the independent assessment of the separate effects of neonatal gonadectomy or neonatal hormone injections.