Experimental evidence is introduced for circularly birefringent and dichroic behavior in aMgF2thin-film helicoidal bianisotropic medium (TFHBM), which is a rotationally inhomogeneous and anisotropic material. Optical rotation (OR) of an incident linearly polarized monochromatic plane wave is observed upon transmission through theMgF2/glassTFHBM/substrate system, and it is accompanied by an ellipticity in the polarization of the transmitted plane wave. Both OR and ellipticity spectra have remarkable features within a narrow wavelength zone not unlike the Cotton effect in isotropic chiral media. The features in the experimental spectra are in accord with theoretical predictions. ©1997 American Institute of Physics.