Two Japanese females complained of cough and bronchorrhea for which chest radiographs showed infiltrate in the lungs. The patients were subsequently diagnosed as having bronchioloalveolar carcinoma by transbronchial lung biopsy. After receiving systemic chemotherapy, their symptoms were slightly improved. A few months later, their bronchorrhea and dyspnea worsened, and they were then treated with gefitinib, a selective epidermal growth factor receptor tyrosine kinase inhibitor. Bronchorrhea and dyspnea were improved within 24 h after treatment with gefitinib where the improvement was evident after 6 h for one patient and 24 h for the other patient. Thereafter, their radiological findings showed gradual improvement. Rapid relief of bronchorrhea preceded the improvement seen by the radiological findings. These observations suggest that gefitinib may inhibit mucin production as well as exert anti-proliferative activity against bronchioloalveolar carcinoma.