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 p-elemene (22.0%), -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 -elemene was tested individually for its repellency and had a med value of 0.23 ? 0.14 mg/cm2 (deet was 0.008 ? 0.001 mg/cm2). this is the first report on the repellent activity of l. montevidensis eo and p-elemene using human-based in vivo assays against ae. aegypti.