SEREX (serological analysis of recombinant tumor cDNA expression libraries) is a technique designed to isolate tumor antigens that have elicited high-titer IgG responses in human hosts. This is an immunoscreening method for gene cloning, with two key features that distinguish it from earlier immunoscreenings used to identify targets in autoimmune diseases. First, the assay was designed, at last originally, to analyze autologous immunological responses to cancer, that is, the tumor cDNA library and the screening serum were obtained from the same patient. Second, the screening is performed with serum samples at high dilution (1:1000-1:100), and the secondary antibody used was specific for human IgG. This ensures that only antigens eliciting high-titer IgG responses will be isolated. This latter feature is important in that a key purpose of SEREX is to identify tumor antigens that have elicited both humoral and cell-mediated immune responses in cancer patients. Several tumor antigens identified by SEREX on various types of cancer indeed showed such characteristics and these antigens are being tested as targets for therapeutic cancer vaccines.