Female BALB/c and B6C3F1 mice were examined after a 3‐wk exposure to dietary estradiol (0, 400, 800, 1600, and 3200 ppb) in a purified diet (AIN‐76A) or a natural‐ingredient diet (NIH‐07). Histological findings, which became more prevalent with increasing estradiol dosage in both mouse genotypes, included vaginal hyperkeratosis and mucoid stroma, uterine inflammation, hydrometra and glandular hyperplasia, and ovarian corpora lutea depletion. At the two lower doses of estradiol, responses were generally more prevalent or severe in mice fed the purified diet than in those fed the natural‐ingredient diet. However, in BALB/c mice, several responses to the two higher estradiol doses were greater when estradiol was given in the natural‐ingredient diet rather than in the purified diet. These responses included corpora lutea depletion, vaginal hyperkeratosis, and uterine inflammation and hydrometra. In B6C3F1 mice, most responses to estradiol at concentrations of 400, 800, and 1600 ppm were more prevalent or severe in mice fed the purified diet than in those fed the natural‐ingredient diet. It can be concluded that several responses to estradiol in mice maintained for a 3‐wk period on a purified diet differed significantly from mice maintained on a natural‐ingredient diet.