Since mouse serine racemase had an amino acid deletion compared with human enzyme, rat enzyme was examined to see whether it had the same deletion. The nucleotide sequence of cDNA encoding rat serine racemase was determined. Deduced amino acid sequence of rat serine racemase had high homology with that of mouse and human enzyme. However, the rat enzyme had the same amino acid deletion as the mouse enzyme. In addition, the rat serine racemase was truncated at the carboxyl terminus and six amino acid residues were less than the other two enzymes. Northern hybridization detected serine racemase transcripts in many tissues.