A case of acute interstitial pneumonia developing during gold therapy is reported. A 67-year-old female with rheumatoid arthritis for about twenty years who received a total dose of 80 mg of gold thiomalate (Shiosol) for about two months, developed high fever and dry cough. Exertional dyspnea developed and chest roentgenogram showed diffuse small nodular and reticular shadows. RA and RAPA tests were positive. Drug lymphocyte stimulation test (DLST) for Shiosol was positive. The dyspnea resolved on administration of methylprednisolone. Chest roentgenogram and CT-scan showed improvement. A total dose of 80 mg of gold thiomalate, as administered in this case, is the minimum dose previously reported in Japan. It has been recently reported that allergic reaction is the mechanism of gold lung. In the present case, positive DLST indicated the existence of many activated lymphocytes, and was very useful in the diagnosis of gold lung.