A study of respiratory symptoms and chest illness in underground coal miners was conducted through data obtained during the first round of the National Study of Coal Workers Pneumoconiosis (NSCWP) epidemiological study. The NSCWP involved more than 9000 miners at 31 mines in all major coal fields in the United States. The data base consisted of questionnaire data on respiratory symptoms, work and smoking histories, demographic characteristics, spirometric data, and estimates of occupational exposure. The data were divided into two groups depending on whether the miner reported producing phlegm for at least 3 months of the year or not. Odds ratios were computed for reporting specific and nonspecific respiratory illnesses and losing time from work. Odds ratios were significantly elevated for nonspecific chest illness, pleurisy, pneumonia, chest injury, and heart trouble. The odds ratios were significantly elevated for smokers compared to nonsmokers and older workers, with decreases in 1 second forced expiratory volume of greater than 30 percent noted. Similar increases, though not as large, were seen for smoking and nonsmoking miners who reported producing phlegm. The length of time spent working underground or at a coal face was longer in older miners, miners who reported producing phlegm, and those reporting a nonspecific chest illness. This correlation was seen in both smokers and nonsmokers and persisted after adjusting for age. This correlation was not seen in workers who reported a specific chest illness. The authors suggest that coal miners who report persistent phlegm production may be experiencing more chest illness and time lost from work than those who do not produce phlegm.