D-3-Hydroxybutyrate dehydrogenase fromPseudomonas putidabelongs to the family of short-chain dehydrogenases⁄reductases. We have determined X-ray structures of the D-3-hydroxybutyrate dehydrogenase fromPseudo-monas putida, which was recombinantly expressed in Escherichia coli,in three different crystal forms to resolutions between and A ˚ .