[en] All-trans-Retinoic acid [11,12-3H(N)] was photochemically isomerized using a fluorescent source to afford a mixture of isomeric retinoic acids, from which 9-cis-retinoic acid[11,12-3H(N)] was isolated by reversed-phase HPLC. The identity of 9-cis-retinoic acid[11,12-3H2] was confirmed by coinjection with the unlabeled acid. (Author)