Probably the most important products now derived from hybridoma technology are monoclonal antibodies, whose development won George Koehler and Cesar Milstein a Nobel prize in 1984. Antibodies are proteins produced by certain white blood cells to fight infection. Each antibody is specific to a particular foreign particle invading the body, such as a bacteria or virus. They inactivate the invaders by attaching themselves to them.

Obviously it would be of great value to medicine if antibodies could be produced in the lab in large amounts. That possibility was always limited, however, by the fact that white blood cells do not survive for very long outside the body. To overcome this problem, Koehler and Milstein "persuaded" some white blood cells to fuse with cancer cells taken from tumors. Fusion is not something cells normally do, but it can be promoted by using chemicals, viruses, or, more commonly nowadays, placing the cells together in a high-frequency electrical field. Hybridoma cells obtained in this way multiply and turn out a continuous supply of antibodies—called monoclonal because they are all descended from one original cell.

Although monoclonal antibodies were originally developed for use in medicine, they have subsequently found numerous applications as precise seek-and-find tools. Designed to attach themselves to one type of particle, and one only, monoclonal antibodies have the ability to unerringly locate and mark any given target in any quantity in a mixture as complex as you care to produce. This quality makes them invaluable for a number of uses, such as the analysis of chemical mixtures, monitoring of