The essential oil profile of maca (Lepidium meyenii) obtained from Lima, Peru, was examined. Steam distillates of the aerial parts of L. meyenii were continuously extracted with pentane and the pentane extracts analyzed by GC/MS. Retention indices and mass spectral data were used to identify 53 oil components. Phenyl acetonitrile (85.9%), benzaldehyde (3.1%), and 3-methoxyphenylacetonitrile (2.1%) were the major components of the steam distilled oil. The oil of L. meyenii was tested for phytotoxic, cyanobactericidal, and antitermite activity. The oil was selectively toxic towards the cyanobacterium Oscillatoria perornata compared to the green alga Selenastrum capricornutum, with complete growth inhibition at 100 microg/ml. Mortality of the Formosan subterranean termite, Coptotermes formosanus, was numerically, but not significantly, higher when held on filter paper treated with maca oil. At 1% (w/w), maca oil also appeared to act as a feeding deterrent to termites. Several minor components of the essential oil of maca including 3-methoxyphenylacetonitrile and benzylthiocyanate were significantly active against the Formosan termite. This is the first report on the essential oil composition of L. meyenii.