Both monoclonal and polyclonal antibodies have been used in ChIP. In general, monoclonal antibodies give lower background signals than polyclonal antibodies. However, monoclonal antibodies may not be suitable for X-ChIP. The epitope may have become masked during cross-linking thus preventing epitope recognition. We would suggest using polyclonal antibodies that will recognize multiple epitopes such that there is an increased chance of immunoprecipitating the protein of interest.