The usefulness of squamous cell carcinoma (SCC) antigen as a tumor marker was investigated in 72 patients with histologically verified non-small cell lung carcinoma (NSCLC). Increased level of SCC-Ag was observed in 41%, mostly in patients with squamous cell carcinoma (69%). Positive serum SCC-Ag was correlated with lymph node metastases and with the stage of disease. The positive rate of SCC-Ag observed in patients without and with nodal metastases was 52.9% and 84.2%, respectively. Positive SCC-Ag level was observed in 50% of Stage I, 71.4% of Stage II and 78.9% of Stage III patients with squamous cell carcinoma of the lung. The study proved that preoperative SCC-Ag determination in patients with squamous cell carcinoma of the lung and the course of levels of this marker during postoperative follow-up was of importance. A high preoperative and postoperative SCC-Ag value suggested a worse prognosis.