The evolution of sexual dimorphism presents a challenge in that two distinct phenotypes must be produced from the same underlying genome. Sex-biased gene expression can resolve this challenge by differential expression of genes from the shared genome. Sex steroids, including testosterone, are one potentially important regulator of sex-biased gene expression related to growth and body size, but are most frequently studied in species where males are larger than females. We used castration surgeries and hormone replacement to assess the impact of testosterone on transcriptome expression in a species where females are larger than males, the eastern fence lizards (Sceloporus undulatus).