The overall goal of the project was to test the hypothesis that <i>Lamium amplexicaule</i> and<i> Lamium purpureum</i>, weedy invasive species to North America, use phytotoxic allelochemicals in interplant competition. The chemical compositions of the essential oils from the aerial parts of <i>L. amplexicaule</i> and<i> L. purpureum</i> have been obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The essential oils and several essential oil components have been screened for phytotoxic activity on lettuce (<i>Lactuca sativa</i>) and perennial ryegrass (<i>Lolium perenne</i>) as well as nematocidal activity against <i>Caenorhabditis elegans</i>, brine shrimp (<i>Artemia salina</i>) lethality, and insecticidal activity against the red imported fire ant (<i>Solenopsis invicta × richteri</i>). <i>L. amplexicaule </i>essential oil was composed largely of α-pinene, β- pinene, 1-octen-3-ol, (E)-caryophyllene, and germacrene D, while <i>L. purpureum</i> oil was dominated by α-pinene, β-pinene, 1-octen-3-ol, β-elemene, and germacrene D. Neither essential oil exhibited notable phytotoxicity or lethality against nema-todes, brine shrimp, or fire ants. It is unlikely, therefore, that the allelopathy observed in these <i>Lamium</i> species is due to volatile phytochemical constituents

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