RESUMEN
Fifty-four hourses, mostly in Bangkok and Nonthaburi, where 54 lung cancer patients had lived for same time were selected for investigating the presence of indoor radon by the charcoal canister method. In only four of these houses were radon level higher than the normal threshold level of 150 Bq.m (i.e. 153, 160, 172 and 283 Bq.m). Thus, the prevalence of elevated radon concentrations was a mere 7.40 percent in contrast with 22.16 percent found in the general survey. Although this finding would apparently suggest a negative relationship between indoor radon concentrations and lung cancer, it is possible that those patients had been exposed earlier to high radon concentrations, perhaps when the buildings were still new. It should be remembered also that exposure to even low radon concentrations dose not rule out the potential hazard of this radioactive gas as a cause of lung cancer. Most houses in this study (92.60%) were constructed of concrete and more than 5 years old. Therefore, it is not surprising to encounter such low radon levels, since rates are usually higher in newer buildings.