On the basis of an in vitro evolutionary process, mirror-image RNA or DNA oligonucleotides can be identified to bind and inhibit pharmacologically relevant target molecules conceptually similar to monoclonal antibodies.Such molecules are termed L-aptamers or Spiegelmers.Several Spiegelmer against a variety of targets have been identified.Currently, three Spiegelmer-based compounds are evaluated in clinical studies.So far, Spiegelmers have been shown to be safe and well tolerated.Moreover, strong signs of efficacy in patients have been reported.The identification of a Spiegelmer candidate and its preclinical and early clinical characterization will be presented.