Conjugated linoleic acids (CLA) are naturally occurring fatty acids that have been recognized to modify prostaglandin (PG) production in specific tissues. So far, no relationship between PG production and CLA has been reported in the brain. Thus, the effects of CLA on cerebral prostaglandin E(2) (PGE(2)) levels and cyclooxygenase (COX)-1 and COX-2 mRNA expression in mice were determined in the present study. Mice given the diet with or without 3% CLA at the age of 9 weeks were mated, reproduced and lactated. Offspring mice given each diet until 25 days and 8 weeks of age were sacrificed and their brains removed. Production of PGE(2) was reduced while COX mRNA was quantitatively increased by CLA supplementation. These results imply that brain PGE(2) production can be reduced by dietary CLA without inhibition of COX gene expression in mice.