Dendrimers are currently under investigation as potential polymeric carriers of contrast agents for magnetic resonance imaging (MRI), scintigraphy and X-ray techniques, i.e. computed tomography (CT). The objective for synthesizing large molecular weight contrast agents is to modify the pharmacokinetic behavior of presently available small-sized compounds from a broad extracellular to an intravascular distribution. Major target indications include angiography, tissue perfusion determination and tumor detection and differentiation. In principle, imaging moieties, e.g. metal chelates for MRI and scintigraphy and triiodobenzene derivatives for CT, are coupled to a dendrimeric carrier characterized by a defined molecular weight. The structures and sizes of these carriers are presently optimized. So far, however, no compound has reached the status of clinical application. Possible hurdles to overcome are synthetic problems such as drug uniformity, reproducible production of pure compounds and analytical issues, e.g. demonstrating purity . In principle, proof of concept for dendrimeric contrast agents as intravascular and tumor-targeting substances seems to have been established. However, a lot of effort is still necessary before a dendrimeric contrast agent will finally be available for wide-spread use in patients.