The essential oil fromHyptis mutabilis(Rich.) Briq., obtained by hydrodistillation of the aerial part of the plants over two consecutive years, and collected at diferent vegetative stages, flowering and flowering-fructification, did not differ in regard to the composition of analyzed sesquiterpenes but showed variation in the relative concentration of one of its constituents. The oil yield decreased from 0.5% during flowering to 0.3% during flowering-fructification (fresh weight basis). It was analyzed by GC and GC/MS. Twenty-four compounds were identified, which represented 93–5% of the oil in the flowering stage and 92.5% of it in the flowering-fructification one. The oil was found to contain β-caryophyllene (14.3–12.0%), germacrene D (14.7–15.3%), curzerene (11.5–12.7%) and bicyclogermacrene (12.1–14.2%) as major compounds.