Fifteen patients with lung cancer were treated by combined preoperative photodynamic therapy and operation. Preoperative photodynamic therapy was performed for the purpose of either reducing the extent of resection or increasing operability. Clinically, five patients had Stage I disease, two had Stage II, seven had Stage III, and one had Stage IV. There were two cases of tracheal invasion from primary foci, three cases of intrabronchial polypoid tumor or invasion of the carina by primary lesions, eight cases of polypoid tumor or invasion of the main bronchus, and two cases of double primary foci. Argon dye lasers were used in this study. Preoperative laser photodynamic therapy was performed 48 to 72 hours after intravenous administration of hematoporphyrin derivative. Therapeutic conditions were 60 to 600 joules for the superficial invasive areas and additional 200 to 800 mW for 8 to 15 minutes for polypoid tumors. Operation was performed 1 to 9 weeks after photodynamic therapy. The initial purpose of photodynamic therapy was achieved in 11 of 15 patients treated. In four of five originally inoperable cases, conversion to an operable condition was achieved. Ten patients were originally candidates for pneumonectomy, and it became possible to reduce the extent of resection to lobectomy or bilobectomy in seven of them. This study suggests that photodynamic therapy may have an important role in combination with operation and other modalities in advanced lung cancers.