This report focuses on the impact of low concentrations of two purported endocrine-disrupting xenobiotic compounds, nonylphenol and methoxychlor, on two freshwater teleosts of the genus Xiphophorus, X. maculatus, commonly known as the platyfish, and X. helleri, commonly known as the swordtail. Nonylphenol exposure increased mortality rates, elicited stress behaviors, decreased body weight and significantly hampered gonadal development and reproductive function. Methoxychlor exposure elicited stress behaviors, decreased body weight and significantly retarded sexual development. This report demonstrates that, even at "acceptable" concentrations, these compounds pose a serious threat to our aquatic ecosystems.