We have evaluated the effects of the acute administration of noncompetitive N-methyl-D-aspartate receptor antagonist, ketamine, on the expression of serine racemase and D-amino acid oxidase mRNAs in several brain areas of rats. The ketamine administration produced a dose-dependent and transient elevation in the levels of serine racemase and D-amino acid oxidase mRNAs in all the brain areas. These findings suggest that there is a relationship between the gene expression of the d-serine-related enzymes and the blockade of the N-methyl-D-aspartate receptors.