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Abstract One of the most important goals of the Italian survey, initiated in 1989, was to promote ad hoc policies to reduce radon exposure of the population. In the survey a statistical representative sample of 5000 dwellings was chosen; two six-month measurements were made of the indoor radon concentration, in combination with one six month measurement of gamma exposure. The results of the radon concentration measurements are reported here they refer to 80% of the sample. The annual mean value was 81.5 Bq.m-3, which is higher than the reported for other industrialised countries. The survey was widely accepted by the families and provided an opportunity to collect information on families and their habits, as well as on the characteristics of the dwellings. The data will make it possible to evaluate the number of houses above a given level. It is up to the political authorities to define such a level on the basis of these data and the economic and social factors.

Few and sporadic measurements are so far available on the characteristics of indoor radon and thoron daughters in typical Mediterranean areas. For this reason, a pilot study is being carried out in Rome, to study the equilibrium factor F and the influence of ventilation rates in realistic domestic environments. Preliminary data show both a significant influence of ventilation on indoor Rn and Tn daughter concentration and a non-negligible contribution of Tn daughters to the annual effective dose of inhabitants.

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