Contents and types of asbestos in fireproofing insulation materials sprayed on ceilings of 127 buildings throughout the U.S. were studied. Asbestos was found to be present in more than 50% of the buildings and chrysotile was the main component identified. Frequency distribution of airborne fiber concentrations was lognormal. During renovation activities by various workers, including sheet-metal workers, carpenters and electricians, average fiber concentrations at workers' breathing zones were less than 2 fibers/cc, but exceeded 0.1 fibers/cc. During removal of sprayed materials, workers were exposed to extremely high concentrations (average 16.4 fibers/cc) when dry methods were used. When wet methods were used during removal, the airborne fiber concentrations were sharply reduced to less than 2 fibers/cc.