The essential oil (EO) of Lantana montevidensis (Spreng.) Briq. (L. sellowiana Link & Otto) was investigated for its chemical composition and mosquito repellent activity. The essential oil obtained by hydrodistillation of aerial plant parts was analyzed by GC-FID and GC-MS. The major constituents were beta-elemene (22.0%), beta-caryophyllene (20.1%), and germacrene D (9.4%). Sesquiterpene hydrocarbons were present in considerable quantities (78.9%) in the L. montevidensis EO, followed by oxygenated sesquiterpenes (8.9%), monoterpene hydrocarbons (7.7%), oxygenated monoterpenes (1.9%), diterpenes (1.2%) and other compounds (0.2%). The oil of L. montevidensis was repellent with a minimum effective dosage (MED) of 0.021 +/- 0.013 mg/cm(2) as compared with that of the positive control N,N-diethyl-3-methylbenzamide (DEET) with a MED of 0.006 +/- 0.001 mg/cm(2)) against Aedes aegypti L. The major compound beta-elemene was tested individually for its repellency and had a MED value of 0.23 +/- 0.14 mg/cm(2) (DEET was 0.008 +/- 0.001 mg/cm(2)). This is the first report on the repellent activity of L. montevidensis EO and beta-elemene using human-based in vivo assays against Ae. aegypti.