Background: In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit higher performance levels compared to females (a difference attributed to sex steroid hormonal influences). Based upon the results from our companion investigation, this study examined the influence of prenatal sex steroid hormone manipulations on VSM in adulthood, as assessed in the radial arm maze. Additionally, the influence of dietary soy phytoestrogens (i.e., the presence of high or low estrogen-like compounds present in the animal's diet) on VSM was examined in combination with the prenatal hormonal manipulations. Results: Radial arm maze performance on a phytoestrogen-rich diet: 1) females treated prenatally with testosterone were masculinized and acquired/performed in a manner similar to control or oil-treated males and 2) males treated prenatally with an androgen receptor blocker (flutamide) were feminized and acquired/performed in a fashion typical of control or flutamide-treated females. When a diet change was initiated in adulthood, control phytoestrogen-rich fed females outperformed control females switched to a phytoestrogen-free diet. Whereas, in control males the opposite diet effect was identified. Furthermore, flutamide-treated males fed a phytoestrogen-rich diet outperformed flutamide-treated males switched to a phytoestrogen-free diet. Conclusions: These results suggest that prenatal hormonal manipulations significantly sex-reverse the normal sexually dimorphic expression of VSM. Specifically, VSM was enhanced in females treated with testosterone and inhibited in males treated with flutamide. Finally, dietary soy phytoestrogens set a bias on learning and memory in these hormonally manipulated animals in a predictable manner and these data confirm and extend the findings in our companion paper (see Lund etal, BMC Neuroscience 2001 2:20).