The enantiomeric excess of limonene and limonene-1,2-epoxide in lemon peel samples is determined. The enantiomers were separated by multidimensional gas chromatography with flame ionization detection and gas chromatography—mass spectrometry in the selected ion monitoring mode. With this system, it is possible to measure limonene-1,2-epoxide, which appears at low concentrations in lemon peel. The enantiomeric excess of R-(+)-limonene in lemon peel is between 97.1 and 97.4% and that of (1S,2R,4R)-(+)-limonene-1,2-epoxide is between 88.0 and 91.9%. The quantitative determination of limonene in lemon peel is carried out using the optical antipode of the limonene to be quantitated as an internal standard. The authors acknowledge a postdoctoral fellowship from the Spanish Ministry of Science and Education. Peer reviewed