Hyptis suaveolens (Lamiaceae) is an annual species which is used for aromatic and medicinal purposes. The species is polymorphic in its essential oil composition, with three distinct chemotypes in El Salvador of which the fenchone-fenchole type will be the focus of this communication. The fenchone-fenchol chemotype showed strong relative changes, especially within the monoterpenes. The main compounds of the essential oil were sabinene, 1,8-cineole, gamma-terpinene, fenchone, fenchol and the sesquiterpene beta-caryophyllene. Due to strong inter-individual differences, these changes are explained based on several individuals separately. Fenchol was found to decrease drastically when leaves enter the last development stage of yellowing, whereas the proportion of the ketone, fenchone, increased. Furthermore, the proportion of sesquiterpenes decreased in older tissues compared to the monoterpenes. These changes were surprising, because it was expected that yellowish leaves would lose compounds with higher vapor pressures, like sabinene and 1,8-cineole.