Since the initial description of techniques to immortalize anti body-producing B-lymphocytes by fusion with tissue culture-adapted myeloma cells, methods have been developed to produce monoclonal antibodies of defined specificity in multiple animal species. Stable hybrids can be readily produced in mice using a number of myeloma and hybridoma cell lines. To obviate the problem of identifying fusion partners in other animal species, xenohybrids have been produced using B-lymphocytes from the relevant species and mouse myeloma cells. The use of xenohybrids has minimized the problem of obtain ing stable antibody-producing hybrids in all species examined thus far. Although alternative techniques are being developed to produce monoclonal antibodies by molecular methods, hybridoma technol ogy will remain the technology of choice for producing monoclonal antibodies for a variety of applications in research and industry. The objective of Monoclonal Antibody Protocols is to provide investigators with a set of methods for producing and using mono clonal antibodies in biomedical, agricultural, and biological sciences. The book is not intended to provide methodology for all possible applications, but rather a series of methods presented in an easy-- follow format that can be used by new and established investiga tors, graduate and postgraduate fellows, and technical staff.