Testosterone levels during early development influence subsequent sex-typical behavior. These influences were initially identified in experimental research on nonhuman species. Additional research—primarily investigating individuals exposed to atypical hormone environments due to genetic disorders or maternal treatment with hormones during pregnancy—suggested that testosterone also influences the development of sex-typical behavior in humans. There is also interest in identifying relations between normal variability in the early hormone environment and normal variability in subsequent behavior. This article reviews studies that have assessed prenatal testosterone exposure in typically developing children using amniotic fluid sampling or maternal blood sampling. It concludes that both these approaches are promising, but both require larger samples than those used in most studies to date. Recommendations for future research also include using outcome measures that show sex differences, analyzing data within each sex, considering the time of day (as well as the time of gestation) when samples were taken, and reporting all the measures evaluated, not just those showing significant effects.