leaf from two guatteria elliptica r. e. fries (annonaceae) specimens were collected at paranapiacaba and caraguatatuba in s~ao paulo (brazil). the essential oils presented (gc/gc-ms), as major compound, spathulenol (53.9%) for the paranapiacaba specimen and caryophyllene oxide (40.9%) for caraguatatuba. the oils showed low antioxidant activity with ec50 = 7.24 +/- 1.03 and 28.68 +/- 5.78 mg/ml, respectively, for paranapiacaba and caraguatatuba specimens. both oils did not show a relevant (mic > 3 mg/ml) antimicrobial activity. however, the paranapiacaba oil presented an important antitumour activity against breast and prostate cancer cells (ic50 = 7.01 +/- 0.23 and 5.35 +/- 0.35 g/ml, respectively) and a low cytotoxicity against normal fibroblast cells (ic50 > 22.27 e ic10 = 18.55 +/- 1.89 g/ml). isolated major compound, spathulenol, showed good activity against mcf-7 and pc-3 with ic50 = 5.38 +/- 0.20 and 2.25 +/- 0.28 g/ml g/ml, respectively.