Rheumatoid arthritis was diagnosed in a 48-year-old woman. She received a gold compound, and 4 weeks after the start of that therapy, interstitial pneumonia appeared. Findings from a muscle biopsy, and high serum CPK and LDH levels indicated that she suffered from polymyositis rather than rheumatoid arthritis. The result of a drug lymphocyte stimulation test (DLST) for the gold compound was more than 200%. Because the usefulness of the DLST for the gold compound in the diagnosis of gold pneumonitis is not thoroughly established, the DLST was also done in patients with rheumatoid arthritis who were receiving the gold compound without side effects, and in normal subjects. Many of the rheumatoid arthritis patients and some of the normal subjects had a positive response to the gold compound. Therefore a positive response on the DLST for the gold compound does not always support the diagnosis of gold pneumonitis.