To study the involvement of testosterone in the development of spatial abilities, testosterone propionate (TP) was administered to male and female rats during the first week after birth. As adults, these rats were trained and tested on the radial arm maze (RAM) or the Morris water maze (MWM). Sex and neonatal TP treatment influenced number of trials to criterion, accuracy, and the use of an adjacent-arm strategy on the RAM, as well as the speed with which the rats learned the location of a hidden platform in the MWM. On both RAM and MWM, control males performed better than control females, but TP treatment reversed this pattern, producing better maze performance in females and worse in males. Neonatal TP effects on MWM performance were also examined in 21-day-old male and female rats. Performance paralleled that of the adults in all but the testosterone-treated male group, which did not differ from control males. The results of this study provide support for the hypothesis that circulating testosterone during brain development may play a role in the development of spatial memory, and suggest that, in the rat, both the sex difference and testosterone influence are present early in life.