Abstract:Leaf sesquiterpene hydrocarbons of greenhouse-grown saplings of Hymenaea courbaril, and Co pat/era officinalis and C. pubi flora were analyzed by GC for seasonal and diurnal variation. Of the suite of essentially the same ses-quiterpenes in leaves of both genera, only the major compounds (caryophyllene and a, P-selinene) and total quantity (yield) were analyzed statistically as they were considered most likely to be of ecological significance. Diurnal variation was minimal in both Hymenaea and Copaifera during the three dates sampled. Both individual tree (genotype) and seasonal variation were different at highly significant levels for caryophyllene, sclinene and yield in both Hymenaea and Copaifera.