The Monoclonal Antibody Core Facility (MACF) provides the following four high quality services not only at a reasonable cost to investigators but also in a timely manner. 1. The generation of new MAbs / hybridomas to a specific antigen of interest. 2. MAb production (in vitro), purification and modification (including conjugation to fluorphores, biotion and enzymes and the fragmentation of MAbs). 3. Mycoplasma testing of tissue culture samples. 4. In vitro production of recombinant/secreted proteins. Monoclonal antibodies (MAbs) are essential tools used in most if not all fields of biomedical research, in the diagnosis of diseases, and in the treatment of diseases such as infections and cancer. The goal of the MACF is to support the research interests of MSKCC investigators by providing key services related to the production, purification and use of MAbs. Over the last 5 years demand for the MACF services has remained consistently high. From July 2005 through July 2006, 61 investigators from 9 out of 10 programs placed orders with the facility for any combination of the services noted above.