The recent outbreak of severe acute respiratory syndrome and the growing potential of an influenza pandemic force us to consider the fact that despite great advances in critical care medicine, we lack the capacity to provide intensive care to the large number of patients that may be generated in an epidemic or multisite bioterrorism event. Because many epidemic and bioterrorist agent illnesses involve respiratory failure, mechanical ventilation is a frequently required intervention but one that is in limited supply. In advance of such an event, we must develop triage criteria that depend on clinical indicators of survivability and resource utilization to allocate scarce health care resources to those who are most likely to benefit. These criteria must be tiered, flexible, and implemented regionally, rather than institutionally, with the backing of public health agencies and relief of liability. This report provides a sample concept of operations for triage of mechanical ventilation in epidemic situations and discusses some of the ethical principles and pitfalls of such systems.