Growth of Pseudomonas aeruginosa PA01 on isomers of hydroxyproline induced the synthesis of an allohydroxy-D-proline dehydrogenase. The enzyme resembled the D-alanine dehydrogenase of this organism in its association with the particulate fraction and its linkage to oxygen through a cytochrome-containing respiratory chain, but differed from this and other bacterial D-amino acid dehydrogenases in its high substrate specificity and low Km.