The essential oil of the Hypericum brasiliense was obtained by hydrodistillation and its composition studied by GC-MS. The oil represented to 0.1% of the dried material and 20 substances were identified, forming 94.17% of the total oil. Sesquiterpenes were the major constituents (93.14%) of the oil and beta-caryophyllene (29.53%) was the main substance. The oxygenated sesquiterpenes in H. brasiliense represented 12.7% of the oil, and caryophyllene oxide (9.95%) was the major constituent of this fraction. Compared with other species of the genus, the composition of the essential oil of H. brasiliense is closer to the composition of H. perfpratum. Copyright (C) 2003 John Wiley Sons, Ltd.1918082