15 Hydroxyprostaglandin dehydrogenase from bovine lung was purified 7.4 times to a specific activity of 1.4 mU/mg of protein. The isoelectric point was estimated at 5.4 and the molecular weight by gel filtration at 40,000. K(m) for prostaglandin E and for NAD was found to be 3.4 µM and 1.1 x 10M respectively. The enzyme was inhibited by indomethacin and aspirin. The indomethacin inhibition was found to be non competitive to prostaglandin E having a K(i) = 1.4 x 10M and a K'(i) = 1.6 x 10M.