Enzymatic activity was studied in blood plasma, erythrocytes and liver tissue homogenate of rats treated with vegetable aromatic substances. 60 rats were kept within 3 months in atmosphere containing naturally occurring concentrations of monarde ester oil. Control animals were maintained in usual atmosphere of vivarium. In liver tissues of control animals glycolytic processes predominated as shown by the data on increased activities of lactate- and glucose-6-phosphate dehydrogenases. At the same time, activity of soluble microsomal enzyme acetyl esterase was decreased in liver tissue, while activity of these esterases was increased in blood plasma, thus suggesting that membrane structures were destabilized. Aromatic fractions of monarde ester oil, introduced into atmosphere, contributed to normalization of the enzymatic reactions studied.