Novel, transient prodrug forms of the phenolic dihydroxy sympathomimetic amines have (i) the structural formula (I): ##STR1## wherein X is O, S or NR. sup. 5 ; n is 1 or 2; R. sup. 1 is the monodehydroxylated residue of a phenolic, nuclear dihydroxy natural sympathetic or sympathomimetic amine when n is 1, and the didehydroxylated residue of a phenolic, nuclear dihydroxy natural sympathetic or sympathomimetic amine when n is 2; R. sup. 2 is selected from the group consisting of straight or branched chain alkyl having from 1 to 20 carbon atoms; aryl having from 6 to 10 carbon atoms; cycloalkyl having from 3 to 8 carbon atoms; alkenyl having from 2 to 20 carbon atoms; cycloalkenyl having from 4 to 8 carbon atoms; alkynyl having from 2 to 20 carbon atoms; aralkyl, alkaryl, aralkenyl, aralkynyl, alkenylaryl, alkynylaryl, loweracyloxyalkyl, and carboxyalkyl, wherein alkyl, aryl, alkenyl and alkynyl are as defined above; saturated or unsaturated monoheterocyclic or polyheterocyclic, or fused heterocyclic, containing from 1 to 3 of any one or more of the hetero atoms N, S or O in each heterocyclic ring thereof and each such ring being from 3- to 8-membered; and mono-or poly-substituted derivatives of the above, each of said substituents being selected from the group consisting of lower alkyl, lower alkoxy, lower acyl, lower acyloxy, halo, haloloweralkyl, cyano, carbethoxy, loweralkylthio, amino, nitro, loweralkylamino, diloweralkylamino, carboxyl, carbamyl, loweralkylcarbamyl, diloweralkylcarbamyl and ##STR2## wherein R. sup. 4 is hydrogen or alkyl having from 1 to 10 carbons; R. sup. 3 is hydrogen, R. sup.