The occurrence and severity of pneumoconiosis were studied in 100 coal miners with rheumatoid arthritis (RA) and compared to findings in a geographically relevant survey of coal workers' pneumoconiosis. Contrary to European reports, miners with RA were not found to have an excessive frequency or severity of pneumoconiosis. In 55 of these men, serum immunoglobulin levels and rheumatoid factor were compared with data from matched RA patients with no history of silica exposure. The immunochemical results were unrelated to the stage of pneumoconiosis, nor did they differ from those in the control group.