The essential oils of lemon grass, geranium, sweet margorum, Brazilian pepper tree, santinica and hazanbil leaves were obtained by steam distillation. The chemical composition of these oils was elucidated by gas liquid chromatography. The essential oils under study were distinguished by having basic components belonging to different organic classes, i.e., aliphatic aldehydes, aliphatic alcohols, cyclic monoterpene alcohol, aromatic hydrocarbons and aliphatic hydrocarbons for lemon grass, geranium, sweet margorum, Brazilian pepper tree, gantonica and hazanbal, respectively. The influence of these essential oils at different levels on Aspergillus parasiticus
growth and aflatoxin production was evaluated. The fungus was allowed to grow on a yeast extract-sucrose media in a stationary culture incubated in the dark at 26± 1°C for 7 days. Administration of the essential oils caused a concomitant decrease in both mycelial dry weight and aflatoxin production. This was entirely dose dependent. In general, the inhibition effect of the oils on A. parasiticus
growth and aflatoxin production followed the sequence: lemon grass > geranium > sweet margorum > hazanbal > santonica > Brazilian pepper tree. It appears that there is a relationship between the chemical structure of the most abundant substances in the essential oils under study and the antifungal potency.