Measurement of Clq-BA and CEA levels in patients with lung cancer may provide additional information about their clinical status discriminating between disease free patients and those with residual disease. Post-operative determination of Clq-BA and CEA levels may assist in defining patients which have poor prognosis. Preliminary evidence suggests that Clq-BA measurement may provide additional prognostic information in a small group of patients with normal CEA values. Finally, the presence of elevated Clq-BA in tumor bearing patients is of fundamental importance in the biology of cancer as it suggests that there are some tumor associated antigens which provoke the production of antibody in the host with the resultant formation of circulating immune complexes. The definition of the nature of the antigen in these immune complexes awaits further study.