Sets out three methods for the determination of the radon content in indoor air. Method A applies to grab samples and requires the collection of a grab sample in a scintillation cell followed by the measurement of its alpha activity. Method B is applicable for short-term sampling periods. The principle consists of adsorption of the radon onto activated charcoal followed by the measurement of the gamma radiation that is emitted. Method C applies to sampling periods of up to a year and employs solid state nuclear track monitoring.