The field of immunotargeting, and the challenges met when this technique is applied in experimental animals or in patients, are reviewed. Even with highly specific monoclonal antibodies, non-specific uptake in normal tissues and high background level of unbound radioactivity in blood and extravascular body fluids remain significant problems. Further experimental work in animal model systems is needed to bring this technique from the state of being an experimental method, with limited clinical application, to a routine diagnostic or therapeutic method. Different animal models are available, and their potential for elucidation of the various methodological problems in radio-immunotargeting are discussed in the present paper. In our laboratory, two intraperitoneal models were devised, having relevance for gynecologic and other forms of intraperitoneal malignancies. These models were elaborated with special emphasis on the possibility for exact measurement of important parameters in immunotargeting reactions. In the first model, hybridoma cells are inoculated intraperitoneally to mimic intraperitoneal carcinomatosis, and the monoclonal antibody produced by the hybridoma is used as serum tumor marker. In the second model the tumor cells are contained within intraperitoneally implanted micropore chambers, resembling a localized tumor. An artificial tumor like this allows control with the antigen load in the target, and measurement of the concentration of the injected antibody in the fluid within the target.