Correlations between radon concentration and indoor gamma dose rate, soil permeability and dwelling substructure and ventilation were studied using data from 84 low rise residential houses collected in an area of enhanced indoor radon concentration. The radon concentrations varied from 30 to > 5000 Bq m(-3). Cross-tabulation, comparisons of means and multiplicative models were used to test the significance of the effects. In this study a quite high percentage of explained variation R2 (68%) was found. It was found that the most important factors were the substructure and the permeability of the soil. Due to the rather small sample size and moderate variation in the uranium content of the bedrock of the area, the effect of the indoor gamma dose rate was not so prominent. The effects of ventilation habits and sleeping with open windows were not detected in this study.