To evaluate the malignancy of lung cancer, nuclear DNA content, AgNORs counts and cathepsin B activity were examined. The survival time of small cell carcinoma patients with limited disease of near diploid is longer than that with limited disease of hyperdiploid pattern. By flow cytometric technique, the proportion of DNA aneuploid pattern were higher in adenocarcinoma than in squamous cell carcinoma. In squamous cell carcinoma, the prognosis of patients with DNA aneuploid pattern was worse. However, there was no significant difference in survival time of adenocarcinoma patients. A good correlation between the AgNORs counts and tumor volume doubling time of non-small cell carcinoma of lung was observed. However, the AgNORs counts were an independent prognostic factor for survival time of patients with lung cancer. The survival time of lung cancer patients with the marked intensity of cathepsin B was significantly shorter than that of patients with negative and/or weak positive staining pattern. The AgNORs value and cathepsin B activity can serve as a pertinent marker for clinical assessment of malignancy of lung cancer.