Lung cancer remains an extremely difficult neoplasm to treat effectively. A large part of our lack of success in dealing with these patients is related to our empiric therapeutic attempts. Slowly our basic understanding of the lung cancers is improving and techniques are becoming available to allow us to better understand the biology of these neoplasms. This volume reviews several areas of interest in regard to the biologic behavior and characteris of lung cancer. tics Chapters deal with the in vitro growth of small cell lung cancer, the inves tigation of growth factors in human lung cancer, the production of mono clonal antibodies against lung cancer and the application and potential use fulness of the human tumor cloning assay in lung cancer management. These avenues of investigation are likely to establish a more scientific basis on which more rational therapy can be designed. Carney and associates have established several continuous small cell lung cancer cell lines in their laboratory. The amine precursor uptake and decar boxylation (APUD) properties of this neoplasm have been confirmed by demonstrating the presence of neurosecretory granules and high levels of the APUD enzyme L-dopa decarboxylase. In addition, several new markers have been documented including bombesin, creatine-kinase BB and neuron specific enolase. These tumor products along with others may be useful serum markers in patients with small cell lung cancer.