Carcinoembryonic antigen (CEA), neuron-specific enolase (NSE) and creatine kinase-BB (CK-BB) were estimated in blood serum of 75 patients with primary lung carcinoma and of 20 patients with nonmalignant lung diseases. CEA and NSE were determined by immunoenzymatic method using monoclonal antibodies (Abbott CEA-EIA and Roche NSE-EIA) and CK-BB was assayed using kits supplied by Boehringer-Mannheim (Monotest CK-NAC aktiviert). Enhanced levels of CEA were observed in 64% of patients with lung carcinoma, mainly with adenocarcinoma. Increased activities of NSE and CK-BB were obtained in 47% and 39% of patients, respectively, principally of those with small cell carcinoma. The CEA level was dependent on the stage of advanced NSCLC carcinoma and of NSE and CK-BB on the stage of advanced SCLC carcinoma. The complex analysis of the three markers has given 100% specificity of test.