Endocrine disrupters are environmental contaminants that can mimic the effects of estrogen. In the wild, they are thought to contribute to disruption of the reproductive systems of animals and have been implicated in the high incidence of hormone-related cancers and diseases in Western populations. Cadmium has been shown to act as a steroidal estrogen in breast cancer cells, forming a high-affinity complex with the hormone-binding domain of the estrogen receptor, but its in vivo effects on reproductive organs have been unclear. In the July 13 Nature Medicine, Michael D. Johnson and colleagues at Georgetown University show that cadmium mimics the in vivo effects of estrogen in the uterus and in mammary glands (Nature Medicine, DOI:10.1038/nm902, July 13, 2003).