Numerous publications show that methoxychlor (MXC), in use today as a DDT substitute, is a reproductive toxicant; it produces deleterious effects on the structure and function of the reproductive organs in exposed species. Exposure of mice (33 mg/kg body weight) to purified (95%) MXC at the time of implantation, or injection, of 5 mg MXC into freshly laid quail eggs prior to artificial incubation, altered sexual arousal and sexual behavior in adult males of both species. When placed near a plastic partition with an estrus female behind it, the MXC-exposed male mice showed no sexual arousal, spent less time near the partition, and exhibited lower testosterone levels. Similarly, adult quail males that were exposed to MXC during incubation showed a lack of sexual interest and copulatory behavior when presented with a receptive female. Some males showed a longer latency period before mounting the female, while others did not show any sexual interest at all. Exposure of salamander embryos to purified MXC at or above 0.3 microM (0.1 mg/l) induced precocial hatching of embryos and reduced the startle response and the distance traveled in response to startle. Exposing hatched larvae to MXC for 3 days also resulted in a blunted startle response. Due to the blunted startle response and decreased avoidance travel, the exposed salamander larvae appear more susceptible to predation and these effects may contribute to amphibian population declines. The results of these studies indicate that developmental exposures to environmental chemicals with hormonal activities produce undesirable behaviors that may affect population dynamics and survivability of exposed species.