Review of EPA's Environmental Monitoring and Assessment Program (EMPA) is an interim report on the committee's review of EPA's Environmental Monitoring and Assessment Program (EMAP). The committee endorses EPA's recognition that long-term ecological monitoring and research are essential and that EPA's statutory responsibilities are not limited to human health. The report concluded that probability-based sampling on a grid is an appropriate method of delineating the extent and providing a periodically updated survey of the nation's ecological resources. The committee also addresses questions concerning the ability of EMAP to achieve its other major goals, i.e., the assessment of status, the detection and characterization of changes or trends in the status of the ecological resources of the country, and the establishment of association between ecological condition and human-induced stresses. Because of the many concerns and substantive questions about the design and implementation of EMAP, the committee recommends that the program not be fully implemented until further evaluations are completed.