Essential oils, extracted from species of the genusZieriausing cold methanol extraction, were used to divide theZieriaspecies into eight groups based on the chemical compositions of their oils using hierarchical cluster analysis. The major components of mostZieriaoils were oxygenated terpenes or other related compounds including car-3-en-2-one, chrysanthenone, eucarvone, methyl eugenol, elemicin and safrole. In several of theZieriaoils the major oxygenated monoterpene made up between 50–60% of the oil composition. Measurements of minimum inhibitory concentration, using an agar dilution method andE. coli, Staph, aureus, Ps. aeruginosaandC. albicansas test organisms, have demonstrated that essential oils fromZieriaexhibit antimicrobial activity. Several of the major oxygenated compounds were tested individually and found, in most cases, to be comparable in bioactivity to the oils in which they occurred.