The U.S. Environmental Protection Agency (EPA) is studying the effectiveness of various ways to reduce high concentrations of radon in houses. This booklet was produced to share what has been learned with those whose radon problems demand immediate action. The booklet describes nine methods that have been tested successfully--by EPA and/or other research groups--on houses with high indoor radon levels. The information presented here is concerned primarily with radon which enters a house from the underlying soil. The first lesson to learn about radon reduction is this: No two houses are alike. Even houses that look the same have small differences in construction that can affect radon entry and the design and effectiveness of reduction techniques. Underlying soils also may vary, even among houses which sit close together. This booklet is intended primarily for homeowners who already have had their homes tested for radon and have decided that they need to take some action to reduce radon levels. (CW)