This study of radon levels in southwest England investigates the correlation between indoor and soil gas radon concentrations and considers the influence of geology, meteorological variables, spatial and depth variations. This paper examines the value of soil gas measurements as an indicator of potential indoor radon concentrations and highlights a number of factors that need to be considered. Only a very weak correlation was obtained between the overall 222Rn concentration in soil gas and inside the home. However, for high soil gas concentrations a stronger correlation with the indoor level was observed. Typically, the soil gas concentration was between a factor of 10 and 1,000 times greater than that indoors. Levels as low as 10 kBq m(-3) in the soil could produce an indoor concentration above the UK action level of 200 Bq m(-3). The moisture content and the inhomogeneity of soil permeability were identified as chiefly responsible for any perturbation of a soil gas concentration associated with a particular geology. Alone, measured soil gas concentrations have only a limited use in the prediction of indoor 222Rn concentrations.