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From symposium on noble gases; Las Vegas, Nevada, USA (24 Sep 1973). Exposures of rats, mice, and hamsters for 90 hours per week to radon daughters nanging from 2000 to 8500 WL, with and without 18 mu g per liter uranium ore dust, caused marked lifeshortening in all three species. Marked reduction in body weights occurred in all three species, with weight losses of 30 to 50% of control animal values in all species after 31/2 months of exposures. Mice exposed to radon daughters and ore dust were particularly susceptible in terms of mortality, although the lungs of these animals showed very little pathological change. Classical radiation pneumonitis with alveolar septal fibrosis and occasional bronchiolar epithelial hyperplasia were the predominant deep lung lesions seen in all species. In contrast to hamsters exposed 30 hours per week to 1200 WL of radon daughters and uranium ore dust, proportionately more of the pathology was seen in the upper respiratory tracts of the hamsters in the present study. The contrast between markedly affected trachea and major bronchi vs. relatively little effects in deep lung was most evident in rats. Findings of severe suppurative laryngitis and bronchitis were frequent in rats, and may have …