We previously cloned a cDNA for mouse cerebellum carbonyl reductase which shows more than 81% homology to the cDNAs for monomeric carbonyl reductases of the rat, rabbit and human, and for pig 20beta-hydroxysteroid dehydrogenase. In the present study, we expressed the recombinant monomeric enzyme (34 kDa and pI 8.3) from the cDNA and compared its properties with the recombinant human enzyme. The mouse and human enzymes showed similar functional properties, although they differed in kinetic constants for carbonyl substrates and in inhibitor sensitivity. Both enzymes lacked glutathione S-transferase activity. Western blot and reverse transcription-polymerase chain reaction analyses showed that the enzyme protein and its mRNA are expressed in various mouse tissues.