Serum Cu, SZn and SCu/Zn ratio were studied in 14 patients with sarcoidosis, 72 patients with pulmonary tuberculosis, 15 patients with pulmonary carcinoma and 50 healthy persons as control. The results were: no significant differences were found between control group and sarcoidosis group in SCu, SZn and SCu/Zn ratio. In tuberculosis group and carcinoma group SCu increased and SZn decreased. Therefore, the SCu/Zn ratio increased significantly. The results suggested that SCu less than 1.2 ppm (means + 2 s), SZn greater than 0.8 ppm (means - 2 s) and SCu/Zn ratio less than 1.5 were helpful for the differential diagnosis of sarcoidosis from pulmonary tuberculosis and pulmonary carcinoma.