An elegant combination of catalytic antibody and a chemical cloaking approach has been used to target two common anticancer drugs specifically to tumor cells. To achieve this, Carlos Barbas and colleagues first masked the reactive functional groups of two known anticancer drugs, doxorubicin and camptothecin, to make them generally less toxic to healthy cells (Proc. Natl. Acad. Sci USA 96, 6925–6930, 1999). Cunningly, the chemical they used to cloak the drugs could not be removed by physiological enzymes, but was readily uncoupled by a catalytic antibody (38C2) that they had previously isolated. Experiments in which they tested the effectiveness of activating the prodrugs in cell culture on colon and prostrate cancer cells showed the antibody to be effective at therapeutically relevant concentrations. In addition, when injected intravenously into mice, the catalytic antibody remained catalytically active over several weeks. Since the chemical cloaking method is generally applicable to many drugs, Barbas suggests the approach would be valuable for targeting aberrant cells with any prodrug of choice, once the antibodies have been adapted for human use.