The aim of this study is to assess the clinical usefulness of serum assays of carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCC), and CYFRA 21.1 in the diagnosis of squamous cell lung cancer. Sixty patients with squamous cell, and twenty-four patients with nonsquamous cell histology of nonsmall cell lung cancer were enrolled in this study. Serum CEA, SCC, and CYFRA 21.1 levels were obtained by commercially available kits. Upper cutoff levels were 10 ng/ml, 3.5 ng/ml, and 3.5 ng/ml, respectively. In squamous cell lung cancer, percentages and 95% confidence interval (CI) of the patients with elevated levels were as follows: for CEA 23.3% (13-36), for SCC 20.0% (10-32), and for CYFRA 21.1 85.0% (73-93). The positivity rate of CYFRA 21.1 was more significant than CEA and SCC in both squamous and nonsquamous cell lung cancer. None of the markers were significant in differentiating squamous/nonsquamous histology. Only tumor marker CEA was significantly elevated in metastatic squamous cell lung cancer (p=0.004). A novel tumor marker CYFRA 21.1 can be used as a reliable tumor marker in diagnosing squamous cell lung cancer. In addition, CEA has an important role in determining metastatic disease.