Aims: The effect of five essential oils (oregano, cinnamon, lemongrass, clove and palmarose) on growth rate, zearalenone (ZEA) and deoxynivalenol (DON) production by Fusarium graminearum strains was assessed. Methods and Results: The influence of the essential oils was tested on irradiated maize at two concentrations (500 and 1000 mg kg(-1)), at different water activity (a(w)) (0.95 and 0.995) and temperature (20 and 30degreesC) levels. At 0.995 a(w) all essential oils tested had an inhibitory effect on growth rate of F. graminearum at both temperatures studied. At this a(w) level, DON production in general was inhibited by all essential oils at 30degreesC and, although palmarose and clove were the only essential oils with statistically significant inhibitory effect on ZEA production, an inhibitory trend was observed when cinnamon and oregano oils were added to maize grain. Conclusions: Antifungal and antimycotoxigenic activity of the essential oils assayed was shown to depend on environmental conditions. Significance and Impact of the Study: It is apparent that essential oils should be considered as alternative preharvest natural fungicides. Further investigation on natural maize grain might be useful to study the effectiveness of these essential oils in the presence of natural mycoflora of maize grain.