Consider this all too common scenario.  After years of research on identifying a potent natural product, performing strain and media optimizations and producing gram quantities for toxicology studies you are told that the compound is too toxic to be used safely in humans.  What do you do next? When this situation occurred at Wyeth during the development of calicheamicn, we decided to exploit this highly potent compound by attaching it to monoclonal antibodies for use in treating cancer.   This presentation will describe the work that went into the identification and characterization of calicheamicin, the improvements in the fermentation process, the chemical modifications performed to allow attachment to proteins and the development and commercialization of the first cytotoxic drug-antibody conjugate.