The essential oil of the aerial parts of Triumfetta rhomboidea was analysed by GC and GC-MS and assayed for its antibacterial and antifungal activities. The main constituents identified were trans-β-caryophyllene (22.4%), kessane (14%) and caryophyllene oxide (13%). The antimicrobial tests showed a mild activity against Escherichia coli and Enterococcus hirae. Copyright © 2005 John Wiley & Sons, Ltd.