With their highly specific affinity for target substances, mAbs resemble mother seabirds picking out their own offspring in a colony of millions of hungry chicks squawking for attention. Even better, mAbs can locate their quarry even if it moves to different locations and hides among different companions. By 1995, about 70 different mAbs were under development by American companies. Half of these mAbs were aimed at treating or diagnosing various forms of cancer. Consider a few examples of the applications that have made this group of molecules such a winner with the pharmaceutical industry.

Diagnosis: Many diseases are connected with the presence of unusual substances in the body, or with either excessive or very low amounts of normal substances. By adding mAbs to samples of blood or other bodily fluids, then fishing them back out with their targets attached, scientists can get very precise measurements of the amounts of specific substances present. Rapid, sensitive, simple, and accurate, this technique lets doctors diagnose diseases in their very early stages before more obvious symptoms appear.

Treatment: Powerful anticancer drugs can be attached to mAbs that specifically seek cancer cells, allowing them to be carried like guided missiles to their target and avoiding unwanted injury to healthy tissues, and the unpleasant side effects of conventional chemotherapy. A recently published example described the use of cancer-seeking and cancer-destroying radioactive monoclonal antibodies against B-cell lymphoma. The treatment, described as "one of the most promising developments in many years," caused tumors to greatly