Contaminated groundwater plumes have formed on the Massachusetts Military Reservation (MMR), a Superfund site on Cape Cod, Massachusetts, as a result of chemical waste disposal. The plumes are of concern to the local people who rely on groundwater as a drinking water source. We used the freshwater turtle as a sentinel species to monitor the reproductive effects of exposure and, by inference, the potential for impact on human health. Our observations of male Chrysemys picta field-trapped from Moody Pond (an impacted site) and Washburn Pond (a reference site) on Cape Cod extended and supported prior observations of reproductive deficits. Morphometric comparison of precloacal length (PCL), which is a sexually dimorphic trait in the turtle, showed that Moody Pond males had a significantly longer PCL than Washburn Pond males. Moody Pond turtles showed reduced testicular weight, which was associated with significantly smaller seminiferous tubule diameter. Epididymal sperm counts were also markedly reduced in Moody Pond animals compared to Washburn Pond animals. Testicular histology and gonial proliferation, as determined by PCNA, were similar in both male populations, while the Moody Pond males had significantly higher germ cell apoptosis than the animals in Washburn Pond. These results suggest that a low-level mixture of xenobiotic contaminants impairs the reproductive functions of turtles exposed to the impacted site but not to the reference site environment.