When attempting to establish libraries of immunoglobulins (Igs) from human subjects during the course of infection or other illness, a number of basic problems present themselves. First, the only source of lymphocytes that can be easily sampled is the peripheral blood in which the representation of antibodies (Abs) against the chosen target is likely to be low. Since direct immunization to increase representation is unethical, alternative means must be devised to drive the proliferation of the clones of interest in vitro. In our own studies of the colorectal cancer (CRC)-associated antigen (Ag) CA-Hb3, a 50-kDa protein that is recognized by monoclonal antibody (MAb), Hb3 (1 ), procedures were developed to drive the proliferation of specific B cells from the blood of patients, through exposure to Ag in vitro. This has enabled generation, through phage display, of recombinant human Abs against CA-Hb3.