The Space Station Freedom (SSF) Environmental Health Care Program is a comprehensive program developed by the Medical Sciences Division at Johnson Space Center to help ensure the health and safety of crewmembers onboard SSF. It encompasses all phases of SSF assembly and operation from first element entry at MB-6 through Permanent Manned Capability and beyond. Responsibilities include definition of acceptability limits for internal contamination and development of environmental monitoring requirements for air and water quality, barothermal parameters, and radiation. On-orbit monitoring requirements are implemented through the Environmental Health System (EHS), a subsystem of the Crew Health Care System. The EHS is comprised of the Microbiology, Toxicology, Water Quality, Radiation, and Barothermal Physiology Subsystems. It provides on-orbit capabilities for air and water quality monitoring and assessment, and for monitoring the SSF internal and external radiation environment. The EHS will support both nominal and contingency SSF operations utilizing fixed and portable hardware deployed throughout the habitable elements of the station. EHS capabilities have been phased to accommodate the restructured SSF program. Other activities supporting the Environmental Health Care Program include preflight assessments of crew microbiology and analysis of shuttle air, water, and surfaces; EHS ground support for real-time nominal and contingency operations; post-flight analysis of archived environmental and clinical samples; and long-term trend analyses for environmental health assessments.