The treatment of choice for most cases of non-small-cell lung cancer is surgical resection; however, which patients with stage IIIA disease are surgical candidates is debatable. For many patients with stage IIIA or IIIB disease, the preferred modality is thoracic radiotherapy. In several randomized prospective trials, the addition of chemotherapy to thoracic radiotherapy produced a significant but clinically small survival advantage over radiotherapy alone. For patients with stage IV lung cancer, no curative treatment or "standard therapy" is available. Accordingly, many patients are offered investigational agents in phase I or II clinical trials. Small-cell lung cancer has a 60 to 90% rate of initial response to available chemotherapeutic agents. Patients with limited disease are generally given combination chemotherapy and thoracic radiotherapy, approximately 50% of whom have a complete clinical remission. Patients with extensive disease (spread beyond one radiation port) also have a high rate of initial response to chemotherapy, but only 20 to 40% have a complete remission and few survive for 5 years. New agents are being tested in previously untreated patients with extensive small-cell lung cancer. Promising new chemotherapeutic agents for lung cancer are being studied in clinical trials. Currently, only 1% of patients with lung cancer in the United States are enrolled in prospective clinical trials. Primary-care physicians are urged to encourage their patients to consider participation in approved prospective clinical trials at reputable medical centers, in an effort to discover new, effective agents with novel mechanisms of action. Information about such studies is available through Physician Desk Query (PDQ) or the cancer hotline (1-800-4-CANCER).