Cyfra 21-1 is a tumor marker based on the determination of watersoluble cytokeratin 19 which is secreted by normal or malignantlytransformed epithelial cells. It is suggested to be a valuable marker innon-small cell lung cancer. This study was conducted to investigate the roleof Cyfra 21-1 in diagnosis, determination of subtypes, staging of lung cancer.35 patients (mean age 56.17± 5.16 Y, male/female: 8/2) (including 25patients with NSCLC and 10 patients with SCLC) and 15 apparently healthycontrols constituted the patients group and control group respectively.Venous blood samples (10 ml) were obtained from all subjects. Cyfra21-1level (cutoff value 3.3 ng/ml) were determined by ELISA-Cyfra 21-1 kit.Cyfra 21-1 did not differ between smoking and non-smoking subjects withincontrol group (p 0.05). The mean values of Cyfra21-1 were significantlyelevated in lung cancer cases irrespective of the cell type (p< 0.05).The specificity and sensitivity of cyfra 21-1 was 100 %, and 40%,respectively. It was significantly elevated in squamous cell carcinoma andadenocacinoma varieties. Sensitivity was 56% in NSCLC, 66.67 % insquamous cell carcinoma, 52.63 % in adenocarcinom and 0% in SCLC cases.