The application of polymeric coatings to uranium mine openings can prevent radon gas from entering the mine atmosphere, thereby reducing miners' exposure to radon daughter products. Of the 46 coating materials tested on uranium ore samples, three were found to be 100 pct efficient as radon barriers, and 22 materials were judged at least 50 pct efficient. Four of the overall best coatings (a latex, an unsaturated polyester, and two water-based epoxies) were then tested in an underground uranium mine in the Ambrosia Lake District of New Mexico to evaluate their sprayability and their in- place barrier efficiency. The coatings exhibited good sprayability, adhesion, and curing in the mine. Radon gas emanation was reduced by 60 pct in one chamber and by 62 pct in the other.