Excess respiratory cancer has been demonstrated among all groups of uranium miners who have had more than 120 Working Level Months of radon daughter exposure. Lung cancer incidence rose with increasing exposure. Factors which might distort the exposure-response relationship were reviewed. Exposure to other agents such as cigarettes probably contributed to the excess, but these factors should not be considered in setting permissible levels. Respiratory cancers are continuing to appear at a high rate among the Study Group even though radon daughter levels have been markedly reduced and most of the Study Group have stopped mining.