abstract the essential oil from hyptis 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 -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.