DHRS4 reduces all-trans-retinal and 9-cis retinal. DHRS4 can also catalyze the oxidation of all-trans-retinol with NADP as co-factor, but with much lower efficiency. Reduces alkyl phenyl ketones and alpha-dicarbonyl compounds with aromatic rings, such as pyrimidine-4-aldehyde, 3-benzoylpyridine, 4-benzoylpyridine, menadione and 4-hexanoylpyridine. DHRS4 has no activity towards aliphatic aldehydes and ketones.