Abstract: The invention provides improved immunoassay techniques for detecting the presence of analytes in a liquid sample. The present immunoassay methods utilize anti-allotypic monoclonal antibodies as capture reagents for primary binding proteins specific for the analytes of interest. The monoclonal antibodies are highly specific for the allotypic determinants present on the primary binding protein. The use of anti-allotypic monoclonal antibodies as capture reagents provides improved levels of specificity and accuracy of the immunoassay, in part because interference from endogenous immunoglobulins in the sample is significantly reduced. The invention further provides anti-allotypic monoclonal antibodies.