We performed intratumoral ethanol injection via a flexible bronchofiberscope in 13 patients with malignant tracheobronchial lesions in order to evaluate its effects on airway dilatation and hemostasis. The results obtained are described below. Immediately after intratumoral injection of ethanol, bronchofiberscopic findings revealed that the tumor turned faintly white, there was a little regression of tumor, and a promising effect was demonstrated on patients with bleeding from tumors. The injected tumor turned necrotic within several days, and histological examination revealed no viable tumor cells in necrotic tissues. The histological anti-tumor effect of ethanol was also demonstrated in experiments with nude mice. This endoscopic treatment was very effective in polypoid tumor protruding into the tracheobronchial lumen, but ineffective in the case of compressed stenosis or obstruction. In conclusion, intratumoral injection of ethanol is considered to be a promising endoscopic treatment for malignant tracheobronchial lesions.