Talarozole (R115866) is an oral systemic all-trans retinoic acid metabolism blocking agent (RAMBA) which increases intracellular levels of endogenous all-trans retinoic acid (RA). Talarozole inhibits both CYP26A1 and CYP26B1 with IC 50 s of 5.4 and 0.46 nM, respectively.