We show that in the visible to near-IR part of the spectrum, normal incidence transmission of circularly polarized light through a nanostructured anisotropic planar chiral metamaterial is asymmetric in the opposite directions. The new effect is fundamentally different from the conventional gyrotropy of bulk chiral media and the Faraday effect. It has a resonance nature associated with a new type of excitation in the metal nanostructure:  the enantiomerically sensitive plasmon.

We demonstrate for the first time a nanostructured planar photonic metamaterial transmitting light differently in forward and backward directions.