The effect of five essential oil components (EOC's) on biofilms were investigated on two pathogenic Listeria monocytogenes isolates. Growth of the biofilm was assessed using the crystal violet (CV) staining assay and the XTT reduction assay. Scanning electron microscopy (SEM) was used to assess the architectural changes of the biofilm. Treatment of a 6 h preformed biofilm with each of the EOC's at a concentration of 1 mg/ml enhanced growth of the biofilm which was confirmed by SEM. Conversely, the presence of the essential oil components caused a reduction in the metabolic activity of the biofilm as shown by the XTT reduction assay.