After presensitization with IV hematoporphyrin derivative (HpD), neoplasms in the tracheobronchial tree of 18 patients were treated by photodynamic therapy (PDT) with 630-nm light from a tunable dye argon laser system delivered through quartz fibers passed through the biopsy channel of a flexible bronchoscope under local anesthesia. Tumor effect was measured by complete response (CR)--no visible tumor in area treated, partial response (PR)--tumor size or degree of obstruction reduced by more than 50% and some response (SR)--tumor or degree of obstruction reduced by more than 20% but less than 50%. One month or less after 30 treatments to 26 areas in 18 patients, there was 40% CR, 57% PR, and 3% SR. All tumors showed at least some response. Since many of these patients had end-stage disease, the effect on the clinical condition and symptoms were evaluated using the Karnofsky Performance Status (KPS), oxygen requirements, and the presence or absence of respiratory symptoms. One month after treatment, 61% were clinically improved, with an increase of the average KPS from 48 to 61. Three patients with stage III primary lung cancer improved from being severely disabled requiring hospitalization to normal activity with effort and lived an average of 3.5 months. One patient with metastatic colon cancer was palliated from bedrest with continuous oxygen to normal activity with no oxygen for 12 months. A patient with hemoptysis and carcinoma in situ remains biopsy- and symptom-free for 34 months. A patient with hemoptysis and cough from breast cancer metastases maintained CR, biopsy- and symptom-free for 7 months. A patient with hemoptysis from recurrence at the bronchial stump maintained CR, biopsy- and symptom-free for 13 months. Six patients with Stage III primary lung cancer with average KPS of 27 (severe) died in the hospital and lived an average of 5 weeks (two CR, two PR, two SR). One patient with atelectasis of the right lower lobe re-expanded 14 days after treatments began.