The clinical significance of multiple tumor marker assay in assisting the diagnosis of lung cancer was assessed in 67 patients with primary lung cancer, and 115 with nonmalignant pulmonary disease. The tumor markers studied were carbohydrate antigen 19-9 (CA19-9), carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), squamous cell carcinoma-related antigen (SCC), and tissue polypeptide antigen (TPA). The positive rates for all of the tumor markers were significantly higher in the lung cancer group than in the nonmalignant pulmonary disease group. The sensitivity was 31-66%, the specificity was more than 90% for all five markers, and the accuracy was 69-82%. Among the markers, the positive rate of CEA was best correlated with adenocarcinoma (Ad), NSE with small cell carcinoma (Sm), SCC with squamous cell carcinoma (Sq), CA19-9 with Ad, and TPA with Ad. In multiple tumor marker assay, as the number of combined markers was increased, the sensitivity of the assay became higher and the specificity became lower, resulting in a lower accuracy. However, when more than two markers were positive, the relative possibility of lung cancer was increased 90-100%. The number of positive tumor markers in multiple tumor marker assay indicated that it would be of auxiliary value for the diagnosis of lung cancer.