Ravid, U., Institute of Field Crops, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 90 000, Haifa, 31-900, Israel
Putievsky, E., Institute of Field Crops, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 90 000, Haifa, 31-900, Israel
Katzir, I., Institute of Field Crops, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 90 000, Haifa, 31-900, Israel

The enantiomeric composition and relative quantity of piperitone in laboratory‐made essential oils and in essential oils and samples of piperitone from commercial sources were determined. High enantiomeric purities of (4R)(‐)‐piperitone were detected in Mentha longifolia (L.) Huds. (Negev type) oil. The (4S)(+)‐enantiomer was detected in peppermint oils and in M. longifolia L. Huds. (Yizre'el Valley) oil in a high enantiomeric ratio. The presence of (4R)(‐)‐piperitone in the oils of some Mentha species is contrary to the postulation that only the (4S)‐enatiomer occurs naturally in the Mentha genus. Copyright © 1994 John Wiley & Sons, Ltd