Following the approval of a few biological products such as insulin and growth hormone produced by recombinant-DNA technology during the early 1980s,therapeutic proteins and monoclonal antibodies in recently year have dominated the field of drug development by biopharmaceutical industry in the United States.Monoclonal antibody,in particular,is considered the most innovative therapeutic class in the 21 st century for treatments of diseases like cancers.With more then 500 candidates in the pipeline,monoclonal antibodies are expected to maintain their dominance in the coming years.However,the complexity of monoclonal antibodies also presents many difficult scientific and regulatory challenges throughout the development cycle.The presentation will focus on the discussion of current regulatory and scientific issues in US for which companies may face during development of monoclonal antibodies.