Identification and development of new monoclonal antibodies and other biological molecules such ad Fab fragments, diabodies and peptides is a key focus of many biotechnology and pharmaceutical companies and academic research department in several therapeutic areas, including oncology, autoimmune disease and infection. Before commencing clinical trials with such products, it is often essential to assess the targeting and/or efficacy effects that are desirable for such biological molecules as well as the potential for off-target effects as a result of non-specific uptake. Here we describe some of the methods that may be used to investigate labeled proteins and similar biological molecules