Like all great discoveries, the procedure developed by George Kohler and Cesar Milstein for immortalizing antibody producing B-lymphocytes (1) is essentially simple, namely, mix B-lymphocytes from the spleen of an immunized rodent with a continuously proliferating B-lymphoma cell line, then induce their membranes to fuse to give a single antibody-secreting cell (hybridoma) that will proliferate indefinitely Importantly, each hybndoma will secrete antibodies with a specificity for only one antigenic epitope, I e., the antibodies are monoclonal It is this property, together with the ability to produce unlimited amounts of antibody, that has revolutionized the use of antibodies in many areas of biological and medical research, and has found important applications not only in clinical diagnosis and therapy, but also for large-scale purification of biological materials Indeed, monoclonal antibodies (MAbs) are essential tools for the cell and molecular biologist and their use has unlocked the doors behind which the function of many proteins and other cellular molecules would have lain hidden