Serum copper (SCu), zinc (SZn) and ceruloplasmin (SCP) concentrations were measured in 199 patients with lung cancer and 81 with nonmalignant lung disease. No significant differences were detected between these groups in the mean concentrations or in the SCu:SZn ratio, nor was any correlation found between the histological type or clinical extent of the tumor and the level of SCu, SZn or SCP. SCu and SCP increased significantly in accordance with the symptomatic stages of Feinstein, and in a parallel manner. These measures were also significantly higher in the patients who died within 4 months of diagnosis than in those who lived for 4 months or longer. SZn was similar throughout and was not predictive of the prognosis. It is concluded that SCu, SZn and SCP determinations are of no help in distinguishing malignant from nonmalignant lung disease and are only of limited importance for estimating the extent of the disease or the prognosis of a patient with lung cancer.