Respiratory disease mortality among uranium (7440611) miners was investigated in a group of 3,366 white and 780 American Indian workers with 1 or more months of underground uranium employment. Detailed occupational and smoking histories were obtained by personal interview during the complete physical examination. An annual census was taken for updating this data. Death certificates were obtained for those deceased. Cumulative radon daughter exposure values were calculated for each miner through the period of investigation. Mortality comparisons between the non white male populations of Arizona and New Mexico and Indian miners and between the United States white male population and white miners were made. For Indian workers, there were 107 deaths observed, versus 123.9 expected. There were significant differences for all malignant neoplasms, 17 observed versus 9.9 expected, with the excess composed of deaths from respiratory malignancies, 11 observed versus 2.6 expected. There were significant decrements in observed white deaths from all heart disease in this group, 2 observed versus 19.2 expected, and vascular diseases, 1 observed versus 6.2 expected. Only 20 of the Indians smoked a pack of cigarettes per day or more. For white miners there were 745 deaths observed versus 512.5 expected. Significant increases were seen for all malignant neoplasms, 206 observed versus 93.9 expected, the excess being due to 144 deaths from respiratory malignancies versus 29.8 expected. There were 80 deaths from cirrhosis of the liver versus 24.9 expected, 140 accidental deaths versus 43.3 expected, the excess being largely non vehicular accidents. Exposure/response curves for bronchogenic cancer showed a clear relationship to cumulative exposure. Small cell undifferentiated cancer was predominant among smoking and nonsmoking miners. Respiratory malignancies were also increased among smokers; however, radiation dose/dependent response plots were also linear, although not so steep, among nonsmokers. The authors conclude that there is a significant excess of respiratory cancer among these uranium miners, which is elevated by cigarette smoking.