Sixty patients with squamous cell carcinoma (SCC) of the lung, including 25 cases with recurrence and 35 cases without recurrence 1 year after operation, were enrolled in this study. The serial serum levels of cytokeratin fragment 19 (CYFRA 21-1) and SCC antigen were measured before operation and 1 week, 1 month, 3 months, 6 months, 9 months, and 12 months after operation for early detection of recurrence. The results revealed that 1) mean serum values of CYFRA 21-1 were significantly higher at early and any times after operation in 25 patients with recurrent SCC when compared with 35 patients without recurrent SCC; and 2) mean serum values of SCC antigen were significantly higher until 9 and 12 months after operation, in 25 patients with recurrent SCC when compared with 35 patients without recurrent SCC. We conclude that CYFRA 21-1 is a better marker than SCC antigen for early prediction of SCC recurrence in the lung.