The Occupational Safety and Health Administration (OSHA) has regulated occupational exposure to asbestos since 1971. Since issuing its first asbestos standard, OSHA has modified it several times in response to new information about the health risk of exposure and concern expressed by workers and public health groups. As each modification has reduced worker exposure and disease risk, each also has introduced new concepts including emphasis on ancillary provisions in standards regulating occupational exposure to toxic substances to enhance worker health; medical removal protection; two attempts at emergency temporary standards; use of historical and objective exposure data to assess worker exposure; the need to eliminate significant risk of disease posed by asbestos; and the presumption of hazard in absence of exposure information. These and other advances have affected all subsequent OSHA standards aimed at reducing occupational exposure to toxic substances.