The essential oils of the fresh leaves of M. ericifolia, M. leucadendron, M. armillaris and M. styphelioides were isolated by a hydrodistillation method and analysed by a gas chromatography/mass spectrometry (GC/MS) technique. The essential oil of M. ericifolia contained methyl eugenol (96.84%) as a major constituent, whereas M. leucadendron was rich in 1,8-cineole (64.30%). The essential oil of M. armillaris was rich in 1,8-cineole (33.93%) followed by terpinen-4-ol (18.79%), whereas M. styphelioides was rich in caryophyllene oxide (43.78%) and (-) spathulenol (9.65%). The essential oils of these species possessed antimicrobial and antifungal activities. M. ericifolia exhibited the highest inhibitory effects against Bacillus subtiles and Aspergillus niger. The antiviral activities of the essential oils against Herpes simplex virus type 1 (HSV-1) were studied in African green monkey kidney cells (Vero) by a plaque reduction assay. The volatile oil of M. armillaris was more effective as a virucidal (up to 99%) than that of M. leucadendron (92%) and M. ericifolia (91.5%). The effects of the essential oils on the antioxidant system status in carbon tetrachloride treated animals were studied. The essential oil of M. armillaris exhibited a marked antioxidant effect, it improved vitamin E, vitamin C and superoxide dismutase parameters so it can be used as a free radical suppressor. Copyright © 2004 John Wiley & Sons, Ltd.