Several antibodies have now been approved for the therapy of cancer. Two of these, rituximab (Rituxan) and alemtuzumab (CAMPATH; ILEX Oncology Inc), are capable of inducing cell death and tumor regressions when given alone. The third, trastuzumab (Herceptin), is not very effective by itself, but does potentiate the activity of paclitaxel (Taxol) and other chemotherapeutic agents. Unfortunately, most antibodies do not kill cancer cells unless they are armed with a cytotoxic agent, such as a radioisotope, a cytotoxic drug, or a protein toxin. Each of these have advantages and disadvantages.