The fatty acid composition of total lipids and total phospholipids of maxillae and mandibles of rats fed an essential fatty acid-deficient (EFAD), marginally FAD (MEFAD), and a control diet was determined. Patterns typical of an EFA deficiency such as a decrease in the levels of linoleic acid and archidonic acid along with concomitant increase in the levels of palmitoleic acid, oleic acid, and 5,8,11-eicosatrienoic acid were observed in the EFAD groups. Concentrations of arachidonic acid were significantly lower in total lipids of mandibles and maxillae of rats in the EFAD, but not in the MEFAD rats, than those of the controls.