[en] The development of new contrast agents results from the optimal interplay of three factors: the chemical properties of the agents, their pharmacokinetics, and their toxicity. The authors have produced three kinds of new potential contrast agents: gadolinium (2.2.1.) cryptate, gadolinium-or iron-labeled polyalkyl methacrylic nanoparticles, and gadolinium-labeled monoclonal antibodies. Properties are tested first by MR measurements on rats. Then MR imaging is performed at 0.35 T, using a surface coil. The use of computerized pharmacokinetic models allows the experimental results to be analyzed comparatively. The results of these trials are the basis for further testing with regard to targeting by monoclonal antibodies, and parmacokinetic modulation by polyalkyl methacrylic nanoparticles