NAD+-dependent 15-hydroxyprostaglandin dehydrogenase catalyzes the oxidation of many prostaglandins at C-15, resulting in a subsequent reduction in their biological activity. We report the isolation of the cDNA for this enzyme. A human placental λgt11 cDNA library was screened using polyclonal antibodies prepared against the human placental enzyme. A 2.5-kilobase cDNA containing the entire coding region for the enzyme was isolated. The cDNA encodes for a protein of 266 amino acids with a calculated Mr of 28,975. Identification of the cDNA as that coding for 15-hydroxyprostaglandin dehydrogenase was based on the comparison of the deduced amino acid sequence with the amino acid sequence of two peptides, one from the rabbit lung enzyme and the other from the human placental enzyme. This cDNA hybridizes with two species of poly(A+) RNA isolated from human placenta: one of 3.4 kilobases and the other of 2.0 kilobases. Isolation of the cDNA for 15-hydroxyprostaglandin dehydrogenase should facilitate studies on the structure, function, and regulation of this enzyme.