Monoclonal antibodies have been used as experimental therapy in humans since the beginning of the 1980s (A.N. Houghton and D. A. Scheinberg. Semin. Oncol. 13:165-179, 1986). They have been hailed as the prototypical magic bullet drug because of their inherent capacity for specificity. Consequently, monoclonal antibodies have many possible therapeutic applications with varied potential for successful outcome. Current review articles discussing monoclonal antibody therapy deal with the application of monoclonal antibodies within specific areas of medicine. The aim of this review is to summarize the current reviews and provide a broader perspective on the medical applications of monoclonal antibodies along with some general principles by which their therapeutic success or failure might be understood.