In order to study the role of calmodulin (CaM) in the proliferation of lung cancer cells, the CaM level of the specimens of 40 cases of primary lung cancers and the DNA content of the specimens of 35 cases of primary lung cancers were determined with phosphodiesterase assay and flow cytometry respectively. It was found that the CaM level of lung cancers was significantly higher than that of host lungs, benign lung diseases and normal lungs (p<0.001) and that it was significantly correlated with the histopathological grading and TNM staging of the lung cancers. It was also found that the cellular DNA content of lung cancers, like the CaM level, was also significantly higher than that of benign lung diseases and normal lungs (p<0.001). There was a significant positive correlation between the cellular DNA content and tissue CaM level in lung cancers (r=0.885). It is believed that CaM plays an important role in the proliferation of lung cancer cells through the mechanism of the promotion of an uncontrolled synthesis of DNA in the cells. Consequently, it is inferred that CaM antagonists may be tried as a chemotherapeutic agent for lung cancer.