Predictive equations were developed for three indices of lung volume for four combinations of race and sex in a working population not exposed to occupational respiratory hazards, as well as similar values for a set of asymptomatic nonsmokers with normal chest radiograph results. Such data should assist in the development of external comparison groups for epidemiological studies. Subjects were selected from the food and kindred products industry, synthetic textile mills and electrical equipment and supplies industry in North Carolina. Approximately 1,200 blue collar workers not considered to be exposed to occupational respiratory hazards were tested by spirometry, were administered a standard questionnaire, and had standard posterior anterior and lateral chest radiographs taken. Prediction equations were established for three indices of lung volume: total lung capacity, residual volume, and their ratio, for various combinations of race, sex, and smoking habits. Asymptomatic nonsmokers with normal radiograph results were then extracted from the overall group, and separate prediction equations were established. The relationship between age and total lung capacity was discussed.