An epidemiological study was conducted by NIOSH on workers occupationally exposed to gold (7440575) mine dust, cummingtonite/grunerite, in a South Dakota facility. The cohort consisted of 440 workers over a 13 year period. Records of workers maintained by federal, state, and local government agencies and records from the Social Security Administration were utilized. Causes of death were interpreted from death certificates. A comparison was made between the observed number of deaths and the number expected on the basis of age, calendar time, and cause specific mortality rates for the general white male population. A total of 71 deaths occurred among the gold miners during the study period. An excess mortality was found in the category of respiratory diseases, and was attributable to non malignant diseases. A significant excess of respiratory tract cancer was demonstrated at each time interval since the beginning of underground mining. Bronchogenic carcinomas were the primary type of lung cancer among the gold miners. Analysis of airborne particles in the mine environment showed the presence of arsenic (7440382), chromium (7440473), and nickel (7440020), mainly from natural ores. The mean fiber content of airborne particulates was 4.14 to 5.5 fibers per meter. The fibers were mainly fibrous amphiboles and fibrous grunerite. Fibrous cummingtonite was present only up to 1 to 2 percent. The median fiber diameter and length were 0.13 and 1.1 micrometer, respectively. The authors conclude that a reevaluation of the current standard for airborne asbestos fibers is needed.