A radon survey was made at five different locations in the Twilight Mine near Uravan, Colorado, to determine changes in radon concentrations in an inactive mine. Data were taken with a continuous monitor set for 1-minute count periods and readings were taken 24 hours a day for 9 days. The 12 readings per station each hour accurately showed how the radon concentration varied during the day. From the data collected from the intake portal to station 4, the average radon emanation rate was estimated at 18 picocuries per second per square foot (pci/sec/ft2). A daily cycle in radon concentration was detected that apparently was related to barometric pressure change.