Based on literature data it can be concluded essential oils originating from plants have antimicrobial activity and have toxic effects in poultry only when administered at very high doses. Antioxidant activity and hypocholesterolemic effects have been reported in chickens. In various studies, but not all, a growth enhancing effect of essential oils has been found. The characteristic flavor of essential oils might play role in poultry performance, but this needs to be confirmed. Essential oils may stimulate the digestion process.