The herbicide atrazine is a potent endocrine disruptor, active in fish and amphibians in the low ppb range. Among other effects, atrazine impairs reproductive development and function including decreased testosterone levels, impaired testicular development, and low fertility/sperm production in male fish, amphibians, and in some reptiles. Atrazine also feminizes fish, amphibians and reptiles resulting in the development of oocytes in the testes and complete feminization. In addition to laboratory experiments, similar effects have been associated with animals in the wild. Although there is some question about how to compare the doses, adverse effects are also observed in laboratory rodents: including prostate disease, low sperm production, and decreased testosterone levels in males and mammary cancer, abortion, and impaired mammary development in females. These effects are all ­consistent with the induction of aromatase, the enzyme that converts testosterone into estrogen, a mechanism that has been demonstrated across vertebrate classes. Despite well over 150 publications from at least 50 independent laboratories ­showing adverse reproductive effects in all vertebrate classes examined, and recent epidemiological studies associating atrazine exposure with low sperm counts in men, breast and prostate cancer, and birth defects, the major manufacturer still maintains that “atrazine has been used safely for 50 years” and the US EPA still struggles with how to evaluate pesticides for endocrine disrupting effects.