From July 1981 to July 1987, hematoporphyrin derivative photodynamic therapy (HpD-PDT) was administered to 36 patients admitted to the National Cancer Center Hospital with roentgenographically occult lung cancer in whom biopsy showed 39 malignant lesions of the trachea and bronchus, although all the lesions could not be localized by the plain chest radiography and computed tomography scanning. The patients received an injection of HpD (2.5 mg/kg body weight) intravenously 72 hours before laser photoirradiation, and all patients underwent at least one session of PDT through a fiberoptic bronchoscope. Among the 39 malignant lesions of the trachea and bronchus, apparent complete responses were obtained in 11 patients with 12 lesions and less than complete responses in 27 lesions. Those with less than complete responses subsequently were treated with surgical or radiation therapy. Of the 36 patients, 16 patients are alive 37 to 109 months after therapy (mean, 65.1 months) with no apparent recurrence or metastasis, and 20 patients have died. Five of the 20 patients died of recurrent lung cancer, and the other 15 died of secondary causes. Regarding treatment complications, only a small amount of excessive airway secretions were observed, and there was no abscess formation in any patient.