Postpubertal injections of a synthetic estrogen, diethylstilbestrol (-DES), and an anti-estrogen, tamoxifen (-Tx), stimulate proliferation of vaginal and uterine epithelial cells of ovariectomized (OVX) adult mice. In vaginae of two groups of OVX mice treated neonatally with DES (DES-) and oil vehicle alone (Oil-), postpubertal injections of DES altered all and 25 out of 37 protein expressions examined, except for keratin polypeptides, respectively. Twenty-one of the DES- and Tx-altered protein expressions showed the same behavior, suggesting that Tx acts as an estrogen agonist on these proteins. Both neonatally Oil- and DES-treated OVX mice given postpubertal injections of DES (Oil-DES and DES-DES) and Tx (Oil-Tx and DES-Tx) showed similar histological changes in the vagina. Epithelial proliferation and superficial cornification were observed in vaginae of five groups of Oil-DES, Oil-Tx, DES-DES, DES-Tx and DES-Oil (given oil postpubertally) OVX mice. In these groups, 13 proteins showed the same behavior, implying that these proteins are related to proliferation and cornification of mouse vagina. The histology of the uterus in DES-Oil OVX mice closely resembled that in Oil-Oil OVX mice; in protein expressions of the uterus, 5 proteins in DES-DES and 7 proteins in DES-Tx OVX mice were different from those in Oil-DES and Oil-Tx OVX mice, respectively. These findings indicate that neonatal DES treatment alters the behavior of the vagina and uterus in response to postpubertally administered DES and Tx.