[en] A multiple time analysis technique has successfully been applied for measurements of environmental levels of ²²⁰Rn using a flow-through Lucas radon detector. The method is based on selective alpha counting of the short-lived nuclide ²¹⁶Pu. Owing to its short half-life (0.145 s), the alpha particle emitted at the decay of a ²²⁰Rn atom will, within a fraction of a second, be followed by an alpha particle from the decay of ²¹⁶Po. By measuring the time interval between successive alpha counts followed by a multiple time analysis, the ²¹⁶Po activity and thereby the ²²⁰Rn activity can be calculated. The method applied to a commercial instrument with a 160 ml Lucas cell as detector shows that a mean ²²⁰Rn air concentration of less than 20 Bq.m^-3 can easily be determined even if the ²²²Rn air concentration is 10 times higher and varies. At lower ²²²Rn levels a ²²⁰Rn concentration less than 1 Bq.m^-3 can be assessed using this technique. The method will be described together with some examples of its practical use. (author)