Odour perception in humans can sometimes discriminate different enantiomers of a chiral compound(1-3), such as limonene. Chiral discrimination represents one of the greatest challenges in attempts to devise selective and sensitive gas sensors. The importance of such discrimination for pharmacology is clear, as the physiological effect of enantiomers of drugs and other biologically active molecules may differ significantly(4). Here we describe two different sensor systems that are capable of recognizing different enantiomers and of qualitatively monitoring the enantiomeric composition of amino-acid derivatives and lactates in the gas phase. One sensor detects changes in mass, owing to binding of the compound being analysed (the ’analyte’), by thickness shear-mode resonance(5-7); the other detects changes in the thickness of a surface layer by reflectometric interference spectroscopy(8-10). Both devices use the two enantiomers of a chiral polymeric receptor, and offer rapid on-line detection of chiral species with high selectivity.