Many achiral molecules can be made chiral by appropriate positioning of an isotope. Accurate detection of this type of chirality has remained elusive, and there is as yet no general method for detection of isotopically chiral species. Here, we present the first application of microwave three-wave mixing to isotopically chiral molecules, detecting enantiomeric excess in ( R/ S)-benzyl-α-D1 alcohol. Our method is expected to be applicable to a broad range of isotopically chiral molecules with a prochiral parent species.