Screening of a cDNA expression library generated from a squamous cell lung carcinoma with autologous serum. Recombinant proteins were screened with preabsorbed patient serum (see Materials and Methods) and antigen-antibody complexes were detected by a color reaction. As shown for clones 11-4 and 26-4, the serum-positive clones were identified in a primary screening (left-hand side). The enrichment of serum-positive clones by replating and subjection to a second round of screening is shown on the right-hand side.