The significance of electronic microscope examination (EM) in the diagnosis of pulmonary neoplasms was evaluated in 40 cases of patients with different kinds of pulmonary neoplasms. In 27 of the 40 cases, final diagnoses were made by light microscope (LM) examination, while in the remaining 13 cases, LM failed to reach definite diagnoses which were established with the help of EM. By analyzing our data, we conclude that in the following situations, EM helps most in the diagnosis of pulmonary neoplasm: 1. diagnosis of neuroendocrinal carcinomas of the lung; 2. diagnosis of some rare pulmonary neoplasm; 3. documentation of the histologic origins of the matastatic pulmonary neoplasms and 4. differentiation of malignant mesothelioma with pleural metastasis of pulmonary adenocarcinoma.