Most of the studies published to date refer to DHRS9 as a retinol dehydrogenase based on the previously published reports (16)(17)(18)36). However, as shown in the present study, DHRS9 is much more efficient toward oxylipins with hydroxyl groups at positions 12 and above than toward retinol or androsterone. It also appears that the members of the SDR9C  family have more divergent functions than the members of the SDR16C or SDR7C families, which primarily specialize in the oxidative (SDR16C) or reductive (SDR7C) metabolism of retinoids. Unlike human DHRS9, human RDH16 displayed much lower rates and higher K m values toward oxylipins than toward androsterone. This study utilized the same Sf9 microsomal preparations of SDRs that were previously analyzed for their activity toward all-trans-retinol and 3α-hydroxysteroids as substrates (34). To determine whether there was a loss of activity during storage, the microsomes were retested with saturating concentrations of all-trans-retinol and androsterone. These assays demonstrated that no significant loss of activity had occurred; thus, the catalytic efficiency of SDRs toward C18-C22 polyunsaturated hydroxylipids can be compared with the previously published **data** on all-trans-retinol and androsterone.