A possible health hazard due to emissions of radon (10043922) daughters in caves was discussed. It was reported to NIOSH that measured concentrations of radon daughters in a number of National Park Service caves were near the OSHA standards for uranium miners. Park Service caves in which radon daughter radiation levels greater than 0.30 working levels (WL) were measured included Carlsbad Caverns National Park, New Mexico; Lehman Caves National Monument, Nevada; Mammoth Cave National Park, Kentucky; Oregon Caves National Monument, Oregon; and Round Spring Cave in Ozark National Scenic Riverways, Missouri. It was also found that at Mammoth Cave, buildings above ground that were cooled with cave air had alpha radiation levels of 0.6WL. OSHA standards for uranium miners that were considered appropriate by the Environmental Protection Agency (EPA) for natural caves were given. These indicated that cumulative exposures should not exceed 4WL months (WLmo) in any calendar year. It is noted that EPA does not regard an individual exposure limit of 4WLmo per year to be safe, since the risk of lung cancer would be expected to double after 10 to 20 years exposure. It is recommended that consideration be given to rotating long term employees working in high radiation areas and that radiation levels in state and privately owned caves be measured.