Ligand-binding assays are the predominant method used for determination of concentrations of biotechnology products in serum or other matrices, as well as for the determination of antidrug antibodies in nonclinical and clinical studies. The challenges regarding the design and validation of these assays are well understood. The US FDA published a Guidance for Industry on Bioanalytical Method Validation and a Draft Guidance for Industry on Assay Development for Immunogenicity Testing of Therapeutic Proteins. The purpose of this article is to highlight specific elements in these guidance documents that should also apply to new methods, discuss the application of new generation ligand-binding methods and LC-MS for these purposes and provide a scientific and regulatory perspective on the specific challenges assessing the pharmacokinetics and immunogenicity of monoclonal antibodies.