In view of possible involvement of fatty acid anilides in toxic oil syndrome (TOS), the effects of linoleic acid anilide (LAA) and heated linoleic acid anilide (HLAA) on the activities of serum enzymes following their oral administration was studied in rats as a function of time. Serum glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) activities decreased significantly in both LAA and HLAA treated rats at day 4. The decreases, however, were confined to only HLAA treated group at later stages with GOT activity showing significant decrease at day 8 and total lactate dehydrogenase (LDH) as well as GOT and GPT activities at day 12. Liver GOT activity at day 4 and LDH activity at day 8 decreased significantly in both LAA and HLAA treated rats. These findings indicate HLAA components may interact with plasma membranes and thereby, reducing the secretion of the enzymes into the serum.