A statistical procedure for monitoring the health status of a community potentially exposed to a hazardous environment is presented. It utilizes two levels of investigation. Level I studies monitor routinely collected vital statistics and routes of community exposure whereas level II studies require additional data collection and are further distinguished by their design and duration. In a level I study, routine vital statistics for specified end points over a specified period of time are monitored, and the observed number of events is compared with the expected number of events for a given population. The statistical model used with this procedure employs a two-step decision rule based on the standardized mortality ratio for the study community. An "alert status" is invoked when the number of events exceeds a prescribed excess. An "action status" is indicated if the excess noted in the initial period persists or if the observed number of events in the initial period greatly exceeds expectation. Should an "action status" be justified, level II studies to determine the likely explanation for the significant excess are initiated. This could include the conduct of a "case-control" study using the exposure data available from monitoring the community.