Enantiomerically pure (1S,5R )-(ÿ)-2,4,4-trimethylbicyclo[3.1.1]hept-2-en-6-one has been found along with chrysanthenone, thymoquinol dimethyl ether and two stereoisomers of dehydrocitral in the essential oil of Laggera tomentosa, which is endemic to Ethiopia. (1S,5R )-(ÿ)-2,4,4-trimethylbicyclo[3.1.1]hept-2-en-6-one has been identi®ed for the ®rst time from a natural source. Chrysanthenone which is the major constituent of the oil (58%), occurs as the (+)- and (ÿ)-enantiomers in a ca 92:8 ratio.