We studied the effect a variety of hormones and chemical stimuli on the activity of low Km aldehyde dehydrogenase (ALDH) in rat H4IIEC3 hepatoma cells and ALDH activity in human HuH7 hepatoma cells. The low Km enzyme in H4IIEC3 cells reflects ALDH2 activity, and the ALDH activity in HuH7 likely represents ALDH5. Of the steroid hormone family, thyroid hormone, progesterone, and dihydrotestosterone increased low Km ALDH activity ∼50%, whereas dexamethasone and estradiol had little effect. Insulin decreased the activity of low Km ALDH. None of these hormones affected the activity of ALDH in HuH7 cells. Among second messengers, 8‐bromo‐cAMP and A23187 increased low Km ALDH activity; HuH7 ALDH activity again was unchanged. Exposure of the cells to 22 mM ethanol reduced low Km activity by ∼20%, whereas hydrogen peroxide, tumor necrosis factor‐α, and interleukin‐β had little effect. Ultraviolet light increased the HuH7 ALDH activity. Retinaldehyde or retinoic acid reduced the HuH7 ALDH activity, but had no effect on low Km ALDH activity. These data suggest that low Km ALDH2 can be regulated by hormones and may not be constitutive as previously thought, and that the HuH7 ALDH is regulated differently.