A case control study of factors associated with coal worker's pneumoconiosis (CWP) in Brazilian coal miners was conducted. The cohort consisted of 161 Brazilian coal miners with radiographic evidence of CWP or suspected CWP. Subjects were matched 1:3 or 1:2 by age and occupational history to miners with normal chest X-rays. Information on cough, phlegm production, breathlessness, recent acute respiratory episodes (RARE), and smoking habits were obtained. Pulmonary function testing was performed. The influence of cough, phlegm production, breathlessness, RARE, smoking, 1 second forced expiratory volume (FEV1), forced vital capacity (FVC), and the FEV1/FVC ratio on the prevalence of CWP was assessed by standard statistical techniques. FEV1s were significantly decreased in CWP cases who had category 1/0 radiographic opacities and who had held only a single mining job. FVCs were significantly decreased in CWP cases with 1/0 category profusions who had worked at two or more different jobs. The prevalence of RARE was significantly elevated in all CWP cases. When miners with suspected CWP who had 0/1 opacities were included in the analysis none of the observed associations were statistically significant. The average number of pack years' smoking did not differ significantly between the cases and referents. The author concludes that these results support the notion that CWP is independent of the effects of coal dust on the bronchial tree.