The presence of malignant cells in lymph nodes is a critical parameter in the staging of lung cancer patients. Assessment of lymph nodes is currently done by histopathology alone. The long-term survival of lung cancer patients who have Stage IB disease (no known lymph node involvement with a tumor greater than 2 cm) is lower than patients who are Stage IA (no known lymph node involvement with a tumor less than 2 cm). Likewise, the survival rates of patients who are judged to be Stage II based on histologically positive level one lymph nodes is often no better than that of higher stage patients who have level two lymph node involvement. These observations suggest that micrometastases are often present in lymph nodes that are not detectable by histological assessment. This proposal will supplement the histopathological examination of lymph nodes with methods that detect occult metastatic cells to determine whether assigning patients to a higher stage more accurately reflects their disease burden. This could affect subsequent treatment and patient outcomes.