Epidemiology is the study of disease incidence rates in humans and epizootiology is the nonhuman animal equivalent. There have been few attempts to integrate epidemiological and epizootiological data from human and nonhuman animal populations coexisting in the same environment. The authors propose that epizootiology research be conducted on chemical pollutants using the framework of the natural environment as a laboratory. These kinds of studies are termed "epizootiologic ecotoxicology." It is suggested that guilds, defined as a group of human individuals or a group of nonhuman species that use their environment in a similar way, be used as experimental probes to assess the effects of chemicals on ecosystems and humans. Improved data would increase the likelihood that effects in exposed populations will attain statistical significance so that high-risk populations can be detected while the number of affected individuals is low. Epizootiologic ecotoxicology information, the product of this research, must be treated as an important component of a unified health evaluation system.